Climate Change Caused by Humans
Modern Day Climate Change

What Science is Telling Us about Climate Change

I highly recommend watching the NSF video series linked above to get a very good overview of what the science is telling us about climate change. Then read on for the scientific details.

Indicators of a Warming World
Figure 7.1: Ten Indicators of a Warming World (NOAA, 2010)

Temperature Trends:

2010 tied 2005 as the warmest year in the instrumental record according to both NASA (2011) and NOAA (2011). According to NOAA, 2010 was the 34th consecutive year with global temperatures above the 20th century average. Figure 7.2 (NASA, 2011) shows that global temperatures continue their warming trend (0.20oC per decade). Figure 7.3 (NOAA, 2011) shows the top ten warmest years on record, nine of which occurred this decade. All 12 of the warmest years on record have occurred since 1997 (Romm, 2010). It should also be noted that the past few years have featured the deepest solar minimum in nearly a century yet the planet is setting warming records.

Global Mean Temperatures (NASA)
Figure 7.2: Global mean temperature anomalies (compared to 1961-1990) from the years 1850 to 2010

Top 10 Warmest Years (NOAA)
Figure 7.3: Top 10 Warmest Global Temperatures

20 of the warmest years on record have occurred in the past 25 years. The warmest years globally are 2005 with the years 2009, 2007, 2006, 2003, 2002, and 1998 all tied for 2nd within statistical certainty. (Hansen et al., 2010) The warmest decade has been the 2000s, and each of the past three decades has been warmer than the decade before and each set records at their end. The odds of this being a natural occurrence are estimated to be one in a billion! (Schmidt and Wolfe, 2009)

Figure 7.4 (NCDC, 2010) shows the global mean temperature and CO2 concentrations from the years 1880 to 2009.

Global Mean Temperatures & CO2 Levels
Figure 7.4: Global mean temperatures and CO2 concentration from 1880 to 2009

Figure 7.5 (Tamino, 2009) clearly shows that surface temperatures north of latitude 60o are warming at an accelerated rate in the past few decades. Tamino (2009) retrieved 113 station records at latitude 60oN or higher with at least 30 years of data.

Arctic Surface Temperatures
Figure 7.5: Arctic surface temperatures since 1880.

Tamino (2009) explains here and here. The analyses show:

  1. The Arctic has experienced a sudden, recent warming.
  2. In the last decade extreme northern temperature has risen to unprecedented heights.
  3. Over the last 3 decades, every individual station north of 70o indicates warming, 13 of 17 are significant at 95% confidence, all estimated trend rates are faster than the global average, some are more than five times as fast.
  4. Oft-repeated claims that "it was warmer in the 1930s" or "it was warmer in the 1940s" are wrong.
  5. The idea that present arctic temperatures are about equal to their 1958 values is wrong.

Kauffman et al. (2009) also shows that the Arctic was experiencing long-term cooling in the past 2000 years according to Milankovitch cycles until very recently. Figure 7.6 reveals this trend shift:

Kauffman et al. (2009) Recent warming reverses long-term arctic cooling
Figure 7.6: Recent warming reverses long-term arctic cooling (Kaufmann et al. modified by University Corporation for Atmospheric Research)

Kaufmann et al. summarizes their study:

The temperature history of the first millennium C.E. is sparsely documented, especially in the Arctic. We present a synthesis of decadally resolved proxy temperature records from poleward of 60 oN covering the past 2000 years, which indicates that a pervasive cooling in progress 2000 years ago continued through the Middle Ages and into the Little Ice Age. A 2000-year transient climate simulation with the Community Climate System Model shows the same temperature sensitivity to changes in insolation as does our proxy reconstruction, supporting the inference that this long-term trend was caused by the steady orbitally driven reduction in summer insolation. The cooling trend was reversed during the 20th century, with four of the five warmest decades of our 2000-year-long reconstruction occurring between 1950 and 2000.

Arctic Ice & Glacial Trends:

Further signs of this warming trend can be seen in the Northern Hemisphere Sea Ice Extent from the National Snow and Ice Data Center. Figure 7.7 shows sea ice extent since 1953. For January 1953 through December 1979, data have been obtained from the UK Hadley Centre and are based on operational ice charts and other sources. For January 1979 through July 2009, data are derived from satellite. Figure 7.8 shows the most current sea ice extent from satellite measurements. Sea ice extent has been dramatically reduced since 1953.

Sea Ice Extent Since 1953
Figure 7.7: Northern Hemisphere sea ice extent since 1953

Sea Ice Extent
Figure 7.8: Current Northern Hemisphere sea ice extent from satellite measurements

Sea ice extent is just part of the picture. Sea ice thickness has also been measured by submarine and ICESat satellite measurement.

Figure 7.9 (Rothrock, et al., 1999) shows sea ice thickness has substantially declined. Using data from submarine cruises, Rothrock and collaborators determined that the mean ice draft at the end of the melt season in the Arctic has decreased by about 1.3 meters between the 1950s and the 1990s.

Sea Ice Draft
Figure 7.9: Mean sea ice draft: Decrease in Arctic sea ice draft for 1958 to 1997.

Since 2004 and there has been a dramatic decrease in thickness according to NASA's press release, NASA Satellite Reveals Dramatic Arctic Ice Thinning dated July, 2009. Some excerpts:

Using ICESat measurements, scientists found that overall Arctic sea ice thinned about 0.17 meters (7 inches) a year, for a total of 0.68 meters (2.2 feet) over four winters. The total area covered by the thicker, older "multi-year" ice that has survived one or more summers shrank by 42 percent.

In recent years, the amount of ice replaced in the winter has not been sufficient to offset summer ice losses. The result is more open water in summer, which then absorbs more heat, warming the ocean and further melting the ice. Between 2004 and 2008, multi-year ice cover shrank 1.54 million square kilometers (595,000 square miles) -- nearly the size of Alaska's land area.

During the study period, the relative contributions of the two ice types to the total volume of the Arctic's ice cover were reversed. In 2003, 62 percent of the Arctic's total ice volume was stored in multi-year ice, with 38 percent stored in first-year seasonal ice. By 2008, 68 percent of the total ice volume was first-year ice, with 32 percent multi-year ice.

Figure 7.10 (NASA, 2009) shows that overall ice thickness and multi-year ice (MY) thickness are decreasing.

Sea Ice Thickness
Figure 7.10: Northern Hemisphere sea ice thickness

Sea Ice Thickness Composite
Figure 7.11: Northern Hemisphere sea ice thickness submarine & ICESAT combined

Figure 7.11 (Kwock & Rothrock, 2009) shows the mean thicknesses of six Arctic regions for the three periods (1958� 1976, 1993�1997, 2003�2007). Thicknesses have been seasonally adjusted to September 15. According to the authors:

"The overall mean winter thickness of 3.64 m in 1980 can be compared to a 1.89 m mean during the last winter of the ICESat record�an astonishing decrease of 1.75 m in thickness. Between 1975 and 2000, the steepest rate of decrease is 0.08 m/yr in 1990 compared to a slightly higher winter/summer rate of 0.10/0.20 m/yr in the five-year ICESat record (2003�2008). Prior to 1997, ice extent in the DRA was >90% during the summer minimum. This can be contrasted to the gradual decrease in the early 2000s followed by an abrupt drop to <55% during the record setting minimum in 2007. This combined analysis shows a long-term trend of sea ice thinning over submarine and ICESat records that span five decades."

Figure 7.12: Current Arctic ice volume anomaly and trend from PIOMAS (Zhang, 2010)

Figure 7.12 above shows sea ice volume calculated using the Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) developed at APL/PSC by Dr. J. Zhang and collaborators. Anomalies for each day are calculated relative to the average over the 1979 -2009 period for that day to remove the annual cycle. This image allows one to visualize recent variations of total Arctic Sea Ice Volume in the context of longer term variability. Daily sea ice volume anomalies for each day are computed relative to the 1979 to 2009 average for that day. The trend for the 1979 to present period is shown in blue. Shaded areas show one and two standard deviations from the trend. 2012 recorded the lowest ice volume of the data set.

2012 Arctic Sea Ice Smashes Record Low A New Climate State: Arctic Sea Ice 2012
Watch this video to see how sea ice minimum just crashed in 2012 - smashing all records.
Arctic sea ice is just fine? Fool Me Once: Artic Sea Ice is Just Fine
Watch this video to see how Lord Monckton and other deniers are trying to fool you about sea ice.
2009 Sea Ice Update Peter Sinclair's Climate Crock of the Week: 2009 Sea Ice Update
Watch this video to learn about the 2009 Arctic sea ice measurements.
Ice Caps Peter Sinclair's Climate Crock of the Week: Ice Area vs. Volume
Watch this video to learn about the difference between ice area and ice volume and why volume is more critical.

Velicogna (2009) used measurements from the GRACE (Gravity Recovery and Climate Experiment) satellite gravity mission to determine the ice mass-loss for the Greenland and Antarctic Ice Sheets during the period between April 2002 and February 2009. During this time period the mass loss of the ice sheets were accelerating with time implying that the ice sheets contribution to sea level becomes larger with time. In Greenland, the mass loss increased from 137 Gt/yr in 2002�2003 to 286 Gt/yr in 2007�2009. Newer data since then shows that Greenland is losing ice even more rapidly. Figure 7.13 (Cook, 2010) shows the ice mass loss in Greenland including the year 2010. The rate of ice mass loss has doubled in the eight years that measurements have been made. Figure 7.14 (Ibid) shows that melt in western Greenland is now accelerating.

Greenland Ice Mass Loss
Figure 7.13: Greenland Ice Mass Loss (Dashed line is average ice mass over the 2002 to 2010 period.)

Greenland Ice Mass Loss rate of Change
Figure 7.14: Greenland Rate of Change of Ice Mass Loss

According to Velicogna (2009), Antarctic (Figure 7.15) ice mass loss increased from 104 Gt/yr in 2002�2006 to 246 Gt/yr in 2006�2009.

Antarctic Ice Mass Loss
Figure 7.15: Antarctic Ice Mass Loss

John Cook at Skeptical Science has several very good summaries of this research. See: An overview of Antarctic ice trends, An overview of Greenland ice trends, and Why is Greenland's ice loss accelerating?.

Glaciers also are used as a signature for climate change. Summer melting, called ablation, controls the mass and extent of glaciers. According to the World Glacier Monitoring Service {WGMS} (2011), preliminary mass balance values have been reported from more than 100 and 80 glaciers worldwide, respectively. The mass balance data are calculated based on all reported values as well as on the data from the 30 reference glaciers in nine mountain ranges in North America and Europe with continuous observation series back to 1980.

According to the WGMS:

The average mass balance of the glaciers with available long-term observation series around the world continues to be negative, with tentative figures indicating a further thickness reduction of 0.5 and 0.6 metres water equivalent (m w.e.) during the hydrological years 2008 and 2009, respectively. The new data continues the global trend in strong ice loss over the past few decades and brings the cumulative average thickness loss of the reference glaciers since 1980 at about 12.5 m w.e.

Figures 7.16 and 7.17 illustrate this ice loss.

Glacial Mass Loss Reference Glaciers
Figure 7.16: Mean annual specific mass balance of reference glaciers

Glacial Mass Loss Reported Glaciers
Figure 7.17: Mean cumulative specific mass balance of all reported glaciers (black line) and the reference glaciers (red line)

Glacial extent is also being monitored. Figure 7.18 (ibid) shows worldwide glacial extent measurements with red being a decrease and blue being an increase in the length of the glacier.

Glacial Extent - Click for Larger Image
Figure 7.18: Glacial extent - retreating (red) and advancing (blue)

In 2005 there were 442 glaciers examined, 26 advancing, 18 stationary and 398 retreating. 90% of worldwide glaciers are retreating. In 2005, for the first time ever, no observed Swiss glaciers advanced. Of the 26 advancing glaciers, 15 were in New Zealand. Overall there has been a substantial volume loss of 11% of New Zealand glaciers from 1975-2005, but the number of advancing glacier is still significant (Ibid). An excellent summary of global glacier data can be found in the UNEP Global Glacier Changes: facts and figures document.

Ocean Heat Content:

Much of the heat that is delivered by the sun is stored in the Earth's oceans while only a fraction of this heat is stored in the atmosphere. Therefore, a change in the heat stored in the ocean is a better indicator of climate change than changes in atmospheric heat. Figures 7.19 and 7.20 (Richardson et al., 2009) and 7.21 (NODC, 2011) clearly show that the oceans have warmed significantly in recent years and the trend is 50% greater than that reported by the IPCC in 2007. The oceans are gaining heat much faster than other regions and more than half of the total heat change in the 42 years between 1961-2003 occurred in the last 10 years The oceans are gaining heat at an increasing rate.

Energy content change of oceans
Figure 7.19: Change in energy content in different components of the earth system for two periods: 1961-2003 (blue bars) and 1993-2003 (pink bars).

Ocean Heat Content Trend
Figure 7.20: Change in ocean heat content since 1951.

Ocean Heat Content Trend
Figure 7.21: Change in ocean heat content since 1955.

There have been a few published articles by Loehle (2009), Pielke (2008), and Willis (2008) that suggest ocean heat content trend since 2003 has either been flat or slightly negative. Of course, a few years does not a trend make but these results appear to be in conflict with the current upward trend. von Shuckmann, Gaillard, and Le Traon (2009) address this apparent conflict in their article Global hydrographic variability patterns during 2003-2008. Their data extends to 2000 m of ocean depth in contrast to Loehle (2009), Pielke (2008), and Willis (2008) data that only extends to 700 m. von Shuckmann, Gaillard, and Le Traon (2009) show that the heat content of the upper 500 m of ocean are subject to strong seasonal and interannual variations primarily due to salinity changes. However, when considering the heat content of the upper 2000 m of ocean, global mean heat content and height changes are clearly associated with a positive trend during the 6 years of measurements. Figure 7.22 (von Schuckmann et al., 2009) below shows this trend.

Ocean Heat Content Trend Upper 2000 m
Figure 7.22: Change in global heat content for the uppermost 2000 m of ocean between 2003 and 2008

Murphy et al. (2009) examined the Earth's energy balance since 1950 including ocean heat content, radiative forcing by long-lived trace gases, and radiative forcing from volcanic eruptions. They considered the emission of energy by a warming Earth by using correlations between surface temperature and satellite data and show that the heat gained since 1950 is already quite significant. Their findings are illustrated below. (Cook, 2009)

Total Heat Content since 1950
Figure 7.23: Total Earth Heat Content from 1950 (ibid)

The oceans are taking in almost all of the excess heat since the 1970s which underscores the point that ocean heat content is a better indicator of global warming than atmospheric temperatures.

Another way to illustrate where the heat is going is shown in Fig. 7.24 below:

Where is the heat going?
Figure 7.24: Components of global warming for the period 1993 to 2003 calculated from IPCC AR4 (Cook, 2010)

A superb discussion on this topic can be found at Skeptical Science's How we know global warming is still happening.

Extreme Weather - Heat Waves, Drought, and Floods:

Heat waves:

According to IPCC (2007), since 1950 the number of global heat waves, warm nights, and warm days has increased while the occurrence of global cold nights and cold days has decreased. North America has been no exception. In recent decades most of North America has been experiencing more unusually hot days and nights and fewer unusually cold days and nights according to United States Global Change Research Program (2009).

An analysis of the European summer heat wave of 2003 found that the risk of such a heat wave is now roughly four times greater than it would have been in the absence of human-induced climate change (Ibid). Russian scientists stated that the July 2010 heat wave there has not been experienced in Moscow in at least 1,000 years. According to Tamino (2010), the average daily high temperature for Moscow for July 2010 was 3.6 standard deviations above the mean of all recorded July values. In other words, the heat wave was a less than 1 chance in 3000 event.

As reported by Heidi Cullen and Claudia Tebaldi of Climate Central:

The summer of 2010 brought intensely hot weather to large portions of the northeastern U.S., central Europe, and Russia. Russia was especially hard hit as a heat wave � with daily high temperatures hitting 100�F � contributing to the deaths of as many as 15,000 people in Moscow while wildfires tore across more than 2,900 square miles in the central and western part of the country. Drought accompanied the record high temperatures decimating more than a quarter of Russia�s grain harvest. Economists estimated the grain losses cost the Russian economy upwards of $15 billion dollars.

Russia Heat Wave
Figure 7.25: Moscow Record-Busting Heat Wave

Nineteen extreme international high temperature records were set in 2010 (Figure 7.26: Climate Central, 2010).

Global Heat Records
Figure 7.26: Countries that Set New Record High Temperatures

2010 now ranks first place for the most number of countries that have set extreme heat records, according to a list supplied to Jeff Master of Weather Underground by Chris Burt. One-third (33%) of those heat records were set in the past ten years. Ten years have had extreme heat records set at five or more countries and all of these have been fairly recent:

  1. 2010: 19 records
  2. 2007: 15 records
  3. 2003: 12 records
  4. 2005: 11 records
  5. 1998: 9 records
  6. 1983: 9 records
  7. 2009: 6 records
  8. 2000: 5 records
  9. 1999: 5 records
  10. 1987: 5 records


Droughts have become more common, especially in the tropics and sub-tropics, since the 1970s. It is likely that the area affected by drought has increased since the 1970s, and it is more likely than not that there is a human contribution to this trend (Ibid). Decreased land precipitation and increased temperatures are important factors that have contributed to more regions experiencing droughts as shown by the Palmer Drought Severity Index (PDSI) in Figure 7.27 (IPCC, 2007).

Palmer Drought Severity Index
Figure 7.27: Palmer Drought Severity Index (PDSI)

The PDSI is a prominent index of drought. Red and orange areas are drier (-PDSI) than average and blue and green areas are wetter (+PDSI) than average. The smooth black curve shows decadal variations. The PDSI curve reveals widespread increasing African drought, especially in the Sahel. Note also the wetter areas, especially in eastern North and South America and northern Eurasia.

The regions where droughts have occurred seem to be determined largely by changes in sea surface temperatures, especially in the tropics, through associated changes in the atmospheric circulation and precipitation. In the western USA, diminishing snow pack and subsequent reductions in soil moisture also appear to be factors. In Australia and Europe, direct links to global warming have been inferred through the extreme nature of high temperatures and heat waves accompanying recent droughts (Bates et al., 2008)

There has been a large drying trend over Northern Hemisphere land since the mid-1950s, with widespread drying over much of Eurasia, northern Africa, Canada and Alaska. In the Southern Hemisphere, land surfaces were wet in the 1970s and relatively dry in the 1960s and 1990s, and there was a drying trend from 1974 to 1998, although trends over the entire 1948 to 2002 period were small. Decreases in land precipitation in recent decades are the main cause for the drying trends, although large surface warming during the last 2�3 decades is likely to have contributed to the drying. Globally, very dry areas (defined as land areas with a PDSI of less than -3.0) more than doubled (from ~12% to 30%) since the 1970s, with a large jump in the early 1980s due to an ENSO-related precipitation decrease over land, and subsequent increases primarily due to surface warming (Ibid). In the U.S. much of the Southeast and West has had reductions in precipitation and increases in drought severity and duration, especially in the Southwest (USGRP, 2009). Figure 7.28 (Ibid) shows the observed drought trends since 1958.

Trend in US Drought
Figure 7.28: Observed drought trends since 1958

For the most recent drought outlook please visit the U.S. Drought Monitor. In his April 27, 2011 US Senate hearing testimony, Dr. Jonathan Overpeck (2011) stated:

  1. There is broad agreement in the climate science research community that the Southwest, including New Mexico, will very likely continue to warm. There is also a strong consensus that the same region will become drier and increasingly snow-free with time, particularly in the winter and spring. Climate science also suggests that the warmer atmosphere will lead to more frequent and more severe (drier) droughts in the future. All of the above changes have already started, in large part driven by human-caused climate change.
  2. However, even in the absence of significant human-caused climate change, the Southwest is prone to drought and megadrought much more severe than droughts witnessed in the last 100 years. The 2000-year record of drought in the region makes it clear that droughts lasting decades are likely independent of human-caused climate change. For this reason, the �no-regrets� strategy is to plan and prepare for droughts no matter the cause � human or natural � and to do so under the assumption that droughts will very likely be hotter and thus more severe in the future than in the past 2000 years.
  3. Scientists and water managers alike, however, should be careful not to assume the currently estimated �worst case� drought scenario will remain so for long. As climate science has advanced in the Southwest, there have been a steady progression of new results that imply that today�s �worst-case� drought scenario is tomorrow�s second-worst case scenario. Water managers should pay particular attention to the emerging science that has been highlighted in the testimony above.

According to Stanford University scientists Diffenbaugh and Ashfaq (2010):

"In the next 30 years, we could see an increase in heat waves like the one now occurring in the eastern United States or the kind that swept across Europe in 2003 that caused tens of thousands of fatalities. Those kinds of severe heat events also put enormous stress on major crops like corn, soybean, cotton and wine grapes, causing a significant reduction in yields."

According to the climate models, an intense heat wave � equal to the longest on record from 1951 to 1999 � is likely to occur as many as five times between 2020 and 2029 over areas of the western and central United States. The 2030s are projected to be even hotter. "Occurrence of the longest historical heat wave further intensifies in the 2030-2039 period, including greater than five occurrences per decade over much of the western U.S. and greater than three exceedences per decade over much of the eastern U.S.," the authors wrote.

US Extreme Hot Seasons
Figure 7.29: Number of Extremely Hot Seasons Per Decade in the US

The authors also forecast a dramatic spike in extreme seasonal temperatures during the current decade. Temperatures equaling the hottest season on record from 1951 to 1999 could occur four times between now and 2019 over much of the United States. The 2020s and 2030s could be even hotter, particularly in the American West. From 2030 to 2039, most areas of Utah, Colorado, Arizona and New Mexico could endure at least seven seasons equally as intense as the hottest season ever recorded between 1951 and 1999. The authors also determined that the hottest daily temperatures of the year from 1980 to 1999 are likely to occur at least twice as often across much of the United States during the decade of the 2030s (Shwartz, 2010).

For more information about projected drought conditions in our future please see Impacts of Climate Change: Freshwater Resources.


According to IPCC (2007):

Globally, the number of great inland flood catastrophes during 1996-2005 was twice as large, per decade, as between 1950 and 1980, while related economic losses increased by a factor of five. Socio-economic factors such as economic growth, increases in population and in the wealth concentrated in vulnerable areas, and land-use change were significant contributors. Floods have been the most reported natural disaster events in many regions, affecting 140 million people per year on average. In Bangladesh, during the 1998 flood, about 70% of the country's area was inundated (compared to an average value of 20-25%). Because flood damages have grown more rapidly than population or economic growth, other factors must be considered, including climate change. The weight of observational evidence indicates an ongoing acceleration of the water cycle. The frequency of heavy precipitation events has increased, consistent with both warming and observed increases in atmospheric water vapor.

In the past century, averaged over the United States, total precipitation has increased by about seven percent, while the heaviest one percent of rain events increased by nearly 20 percent. This has been especially true in the Northeast, where the annual number of days with very heavy precipitation has increased most in the past 50 years, as shown By Figure 7.30 (USGRP, 2009). Extended periods of heavy precipitation have also been increasing over the past century, most notably in the past two to three decades in the United States (Ibid).

Increases in heavy precipitation in the U.S.
Figure 7.30: Increases in heavy precipitation in the U.S.

Figure 7.31 (EPA, 2010) shows that the percentage of annual precipitation falling in single extreme events is increasing.

Increases in heavy precipitation events in the U.S.
Figure 7.31: Percentage of annual precipitation falling in single extreme events

Min, et al. (2011) investigated heavy precipitation events in the United States between 1951 and 1999 and found:

Human-induced increases in greenhouse gases have contributed to the observed intensification of heavy precipitation events found over approximately two-thirds of data-covered parts of Northern Hemisphere land areas. Changes in extreme precipitation projected by models, and thus the impacts of future changes in extreme precipitation, may be underestimated because models seem to underestimate the observed increase in heavy precipitation with warming.

Pall, et al. (2011) analyzed the United Kingdom floods of autumn 2000 - the wettest autumn in England and Wales since records began in 1766. Their analysis showed:

...that it is very likely that global anthropogenic greenhouse gas emissions substantially increased the risk of flood occurrence in England and Wales in autumn 2000...The precise magnitude of the anthropogenic contribution remains uncertain, but in nine out of ten cases our model results indicate that twentieth century anthropogenic greenhouse gas emissions increased the risk of floods occurring in England and Wales in autumn 2000 by more than 20%, and in two out of three cases by more than 90%.

According to NOAA, not only was 2010 the hottest year on record, it was also the wettest year on record for the globe. There were some very notable flooding events in 2010 including, among others:

For more information about projected flood conditions in our future please see Impacts of Climate Change: Freshwater Resources.

How Can Warming Cause Both Drought and Floods?

This is a common question. Think of the atmosphere as a sponge and temperature controls the size of that sponge. A warmer world means a bigger sponge which means more water can be in the air. Storms are the hands that squeeze that sponge so when the sponge is full, more rain and floods result. Global warming is making our sponge bigger and bigger and that is why flooding is getting more frequent and more severe. Areas that have weather conditions that encourage clouds and precipitation (persistent rising air and lower pressure) will get even wetter in a warmer world.

What does one do to turn liquid water into water vapor? Add heat, of course. As the planet warms, water on land will evaporate at a greater rate which means less liquid water is left behind. Areas that are already dry due to normal weather conditions that lead to cloudless skies (persistent sinking air and higher pressure) cannot get this water back. Furthermore, many dry areas get their water from rivers, lakes and reservoirs, and melting winter snow pack. Rivers, lakes, and reservoirs will lose water in a warming world and with a shorter winter and potentially less snowfall, there will be little runoff left in the hottest summer months when it is most needed.

In short, wet regions will get wetter and dry regions will get drier.

U.S. Climate Extremes Index (CEI):

The U.S. CEI is the arithmetic average of the following five or six# indicators of the percentage of the conterminous U.S. area:

  1. The sum of (a) percentage of the United States with maximum temperatures much below normal and (b) percentage of the United States with maximum temperatures much above normal.
  2. The sum of (a) percentage of the United States with minimum temperatures much below normal and (b) percentage of the United States with minimum temperatures much above normal.
  3. The sum of (a) percentage of the United States in severe drought (equivalent to the lowest tenth percentile) based on the PDSI and (b) percentage of the United States with severe moisture surplus (equivalent to the highest tenth percentile) based on the PDSI.
  4. Twice the value of the percentage of the United States with a much greater than normal proportion of precipitation derived from extreme (equivalent to the highest tenth percentile) 1-day precipitation events.
  5. The sum of (a) percentage of the United States with a much greater than normal number of days with precipitation and (b) percentage of the United States with a much greater than normal number of days without precipitation.
  6. * The sum of squares of U.S. landfalling tropical storm and hurricane wind velocities scaled to the mean of the first five indicators.

Figure 7.32 (Ibid) shows that in the United States, extremes in climate are on the increase since 1970.

Unites States Climate Extremes Index
Figure 7.32: United States Climate Extremes Index

Sea-Level Rise:

Sea-level rise due to global warming is a serious threat, especially to coastal communities in developing countries. Sea level gradually rose in the 20th century and is currently rising at an increased rate, after a period of little change between AD 0 and AD 1900. Sea level is predicted to rise at an even greater rate in this century, with 20th century estimates of 1.7 mm per year (IPCC, 2007). When climate warms, ice on land melts and flows back into the oceans raising sea levels. Also, when the oceans warm, the water expands (thermal expansion) which raises sea levels. Figure 7.33 (IPCC, 2007) shows the projected sea-level rise through AD 2100.

Sea Level Rise
Figure 7.33: Projected sea-level rise through AD 2100

Figure 7.34 (Richardson et al., 2009) shows that IPCC 1990 projected sea level increases were too conservative. The latest observations show that sea levels have risen faster than previous projections.

Sea Level Rise Newest Projection
Figure 7.34: Observed sea-level rise between 1970 and 2008 compared to IPCC projections

According to The Copenhagen Diagnosis (2009):

80% above past IPCC predictions. By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4 exceed 1 meter 2 meters sea-level rise by 2100 several meters of sea level rise must be expected

Figure 7.35 (Colorado Center for Astrodynamics Research) shows the current sea level change data using seasonally adjusted values from TOPEX and Jason while figure 7.36 (Sato & Hansen, 2010) shows mean sea level rise over the past 140 years.

Sea Level Rise
Figure 7.35: Current measured sea level change

Sea Level Rise since 1870
Figure 7.36: Sea level rise since 1870.

Mazria & Kirshner (2005) in Nation Under Siege: Sea Level Rise at Our Doorstep, a coastal impact study, show that beginning with just one meter of sea level rise, US cities would be physically under siege, with calamitous and destabilizing consequences. One can view the impact of sea level rise of various US cities at their interactive Website. An example is shown below for Miami Beach, FL today (Figure 7.37) vs. in the year 2100 (Figure 7.38) with a 1 meter sea level rise.

Miami Beach today
Figure 7.37: Miami Beach today

Miami Beach 2100
Figure 7.38: Miami Beach in 2100 with a 1 m sea level rise

Lemonick (2010) writes in the article The Secret of Sea Level Rise: It Will Vary Greatly by Region:

As the world warms, sea levels could easily rise three to six feet this century. But increases will vary widely by region, with prevailing winds, powerful ocean currents, and even the gravitational pull of the polar ice sheets determining whether some coastal areas will be inundated while others stay dry.

Hanson et al. (2008) believe that it is quite possible Earth could end up ice free with CO2 levels of 350 ppm which is well below where we currently are. Because the melting of Antarctic ice takes centuries there is time to lower the "tipping point" level of CO2 before it is too late. When Antarctica was last ice-free, sea levels were 70m (~230 feet) higher than today.

Climate Change and Hurricanes:

A recent paper published by some of the top hurricane researchers in the field (Knutson, et al. 2010) concludes:

...future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2-11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6-34%. Balanced against this, higher resolution modelling studies typically project substantial increases in the frequency of the most intense cyclones, and increases of the order of 20% in the precipitation rate within 100 km of the storm centre.

There has been an observed increase in tropical cyclones (TC) since the mid-1990s. Warmer oceans have played a significant role in this increased frequency. A new study by Emanuel (2010) suggests that lower stratospheric cooling may also be responsible for the uptick in activity and intensity. Climate models may be underestimating future hurricane frequency and intensity because they do not appear to include the impact of stratospheric cooling. Emanuel's research suggests that there may be more hurricanes in the future despite the current consensus of a 6-34% decrease in frequency.

By 2100, the climate is expected to warm 5 oC to 6 oC or more above pre-IR values. During the Pliocene, about 2.5 to 5 million years ago, CO2 levels were comparable to today's levels (near 400 ppm) and the climate was about 3 oC to 5 oC warmer than pre-IR. Geographically, the Earth was also very similar to today so the Pliocene offers a glimpse of what the world may look like by the year 2100. Federov, Brierley, & Emanuel (2010) modeled the expected TC activity in the early Pliocene world. Figure 7.39 (Ibid) is a comparison of modern TC activity (a) and that of the Pliocene (b). This image is a sobering look at what may lie ahead in our world by 2100.

Hurricanes Today and during Pliocene
Figure 7.39: Tracks and intensity of modern tropical cyclones (a) and during early Pliocene (b).

Vechi, Swanson, and Soden (2008) conclude that predicting the future of hurricane activity is at a crossroads. Vechi et al. compared the observed relation of the power dissipation index (PDI) vs. sea-surface temperatures (SST) in the main development region of Atlantic hurricanes. (PDI is the cube of the instantaneous tropical cyclone wind speed integrated over the life of all storms in a given season; more intense and frequent basinwide hurricane activity lead to higher PDI values.) There are two very different futures depending on whether absolute SST or relative SST controls PDI.

Figure 7.40 (ibid) shows PDI anomalies based on absolute SST.

PDI anomolies based on absolute SST
Figure 7.40: PDI anomalies based on absolute SST

By 2100, the lower end of the model projections shows a PDI comparable to that of 2005, when four major hurricanes (sustained winds of over 100 knots) struck the continental United States, causing more than $100 billion in damage. The upper end of the projections exceeds 2005 levels by more than a factor of two. Combined with rising sea levels, coastal communities face a bleak future if absolute SST determines hurricane activity and strength.

Figure 7.41 (ibid) shows PDI anomalies based on "relative SST" which is the SST in the tropical Atlantic main development region relative to the tropical mean SST.

PDI anomolies based on relative SST
Figure 7.41: PDI anomalies based on relative SST

A future where relative SST controls Atlantic hurricane activity is a future similar to the recent past, with periods of higher and lower hurricane activity relative to present-day conditions due to natural climate variability, but with little long-term trend. Even in this scenario, rising sea levels will still allow hurricanes to do more damage in the future than in present day.

Because the correlation of PDI vs. absolute SST and PDI vs. relative SST are equivalent, Vechi et al. conclude that more research is needed in this area.

2010 was a near-record Atlantic hurricane season with 19 named storms, 12 hurricanes, and 5 major hurricanes blowing away 2009 which had only 9 named storms. 2010 was not remembered by most in the public as being a very active hurricane season because few of the storms made landfall. One can only imagine if the reverse were true and many of these storms had hit. (See Figures 7.42, 7.43, 7.44 from The Weather Channel)

2010 Hurricane Scorecard
Figure 7.42: 2010 hurricane scorecard

Top 3 Hurricane Years
Figure 7.43: Top 3 hurricane years

2010 Hurricane Tracks
Figure 7.44: 2010 hurricane tracks

Realclimate's Atlantic Tropical Cyclone Records � Trends and Ephemerality (June, 2010) is a very good synopsis of what is known and not known about climate change and tropical cyclone projections.

IGBP Climate-Change Index:

IGBP Climate Change Index
Figure 7.45: IGBP Climate-Change Index (Click for larger image)

The IGBP Climate-Change Index brings together key indicators of global change: atmospheric carbon dioxide, temperature, sea level and sea ice. It will be released annually. The index gives an annual snapshot of how the planet's complex systems - the ice, the oceans, the land surface and the atmosphere - are responding to the changing climate. The index rises steadily from 1980 - the earliest date the index has been calculated. The change is unequivocal, it is global, and it is in one direction - up!

Each parameter is normalized between -100 and +100. Zero is no annual change. One hundred is the maximum-recorded annual change since 1980. The normalized parameters are averaged. This gives the index for the year. The value for each year is added to that of the previous year to show the cumulative effect of annual change. (IGBP Climate-Change Index, 2010)

Major Weather Events in the 2000s
Figure 7.46: Major Weather Events in the 2000s (Connor, 2011)

2010 was a year of significant climate anomalies. (Cick for excellent graphic and text summary from NOAA.)

Please also visit NASA's Climate Change: Key Indicators for some excellent up-to-date images showing the changing climate.

Next: Impacts of Climate Change

Scott A. Mandia
Professor - Physical Sciences
T-202 Smithtown Sciences Bldg.
533 College Rd.
Selden, NY 11784
(631) 451-4104

Last Updated: 11/1/18