The information on this page is intended to help you when writing to the media or to your government representative about the climate issue. Each science-based fast fact is followed by its web source.

Summary_Quote

Greenhouse Gases (GHG) - Drivers of Climate Change

Recorded Climate Change: 

Warmest Years

Ocean Temperatures

Sea Level Rises

Ocean Acidification

Arctic Ice

Antarctic Ice

Precipitation

Extreme Weather

Permafrost

Irreversible Climate Change

Tipping Points

About the Sources

Summary Quote

According to the IPCC Climate Change Synthesis Report (p.8):

“Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level.”  http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf 

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Greenhouse Gases (GHG) - Drivers of Climate Change

• The global atmospheric concentration of CO2 increased from a pre-industrial value of about 280 parts per million (ppm) to 379ppm in 2005. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Human activities result in emissions of four long-lived GHGs: CO2, methane (CH4), nitrous oxide (N2O) and halocarbons (a group of gases containing fluorine, chlorine or bromine). http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Global atmospheric concentrations of CO2, methane and nitrous oxide have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice cores spanning many thousands of years. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• The atmospheric concentrations of CO2 and methane in 2005 exceed by far the natural range over the last 650,000 years. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Global increases in CO2 concentrations are due primarily to fossil fuel use, with land-use change providing another significant but smaller contribution. It is very likely that the observed increase in methane concentration is predominantly due to agriculture and fossil fuel use. The increase in nitrous oxide concentration is primarily due to agriculture. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Global GHG emissions due to human activities have grown since pre-industrial times, with an increase of 70% between 1970 and 2004. Its annual emissions have grown between 1970 and 2004 by about 80%, from 21 to 38 gigatonnes (Gt), and represented 77% of total anthropogenic GHG emissions in 2004. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• The rate of growth of CO2 emissions was much higher during the recent 10-year period of 1995-2004 (0.92 GtCO2-eq per year) than during the previous period of 1970-1994. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• The largest growth in GHG emissions between 1970 and 2004 has come from energy supply, transport and industry, while residential and commercial buildings, forestry (including deforestation) and agriculture sectors have been growing at a lower rate. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Despite the decrease in global energy intensity (-33%) during 1970 to 2004, its effect on global emissions has been smaller than the combined effect of global income growth (77%) and global population growth (69%); both drivers of increasing energy-related CO2 emissions. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• The long-term trend of declining CO2 emissions per unit of energy supplied reversed after 2000. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• In 2004, UNFCCC Annex I countries (Industrial Countries) held a 20% share in world population, produced 57% of the world’s Gross Domestic Product based on Purchasing Power Parity (GDPPPP) and accounted for 46% of global GHG emissions. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

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The following is from Surging Greenhouse Gas Emissions - Pew Centre Update (July 2006 – June 2009) and Copenhagen Diagnosis, Executive Summary. 2009

• Global carbon dioxide emissions from fossil fuels in 2008 were nearly 40% higher than those in 1990. Even if global emission rates are stabilized at present–day levels, just 20 more years of emissions would give a 25% probability that warming exceeds 2ºC. Even with zero emissions after 2030. Every year of delayed action increases the chances of exceeding 2ºC warming. http://www.copenhagendiagnosis.org/executive_summary.html

• Unmitigated CO2 emissions will likely generate greater warming than previously estimated. Recent observations reveal that CO2 emissions from human activities grew faster over the past decade than the IPCC previously expected. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• A 2007 study by Canadell et al. estimated that the fraction of CO2 emitted by human activities that stays in the atmosphere (the airborne fraction) is growing over time. Because of the accelerating emissions and the increasing airborne fraction, atmospheric CO2 concentration increased at a rate of 2 ppm per year from 2000 to 2007, 33 percent faster than in the 1990s. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• A recent study by analysts at MIT found that when a climate model was updated to include the most recent understanding of socio-economic development, the carbon cycle, and natural climate drivers, the output of the model showed twice as much global warming at the end of the current century than before the model was updated, 9.4 °F (5.2 °C) in the updated model run compared to 4.3 °F (2.4 °C) before the update (Sokolov etal. 2009). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• Carbon Dioxide levels in the atmosphere for 2009 (387 parts per million) are the highest they have been in about 15 million years. Source: NOAA Earth System Research Laboratory (ESRL) Mauna Loa Observatory.

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Recorded Climate Change

Warmest Years

• Eleven of the last twelve years (1995-2006) rank among the twelve warmest years in the instrumental record of global surface temperature (since 1850). http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• The temperature increase is widespread over the globe and is greater at higher northern latitudes. Average Arctic temperatures have increased at almost twice the global average rate in the past 100 years. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Temperatures this decade have been higher than any other decade on record, and one degree Fahrenheit higher than average temperatures in the 20th century. NASA Goddard Institute for Space Studies (GISS) Surface Temperature Analysis.

Ocean Temperatures

Sea Level Rises

• Observations since 1961 show that the average temperature of the global ocean has increased to depths of at least 3000m and that the ocean has been absorbing over 80% of the heat being added to the climate system. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Since 1993 thermal expansion of the oceans has contributed about 57% of the sum of the estimated individual contributions to the sea level rise, with decreases in glaciers and ice caps contributing about 28% and losses from the polar ice sheets contributing the remainder. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Satellites show great global average sea-level rise (3.4 mm/yr over the past 15 years) to be 80% above past IPCC predictions. This acceleration in sea-level rise is consistent with a doubling in contribution from melting of glaciers, ice caps and the Greenland and West-Antarctic ice-sheets. http://www.copenhagendiagnosis.org/executive_summary.html

• By 2100, global sea-level is likely to rise at least twice as much as projected by Working Group 1 of the IPCC AR4, for unmitigated emissions it may well exceed 1 meter. The upper limit has been estimated as ~2 meters sea-level rise by 2100. Sea-level will continue to rise for centuries after global temperatures have been stabilized and several meters of sea level rise must be expected over the next few centuries. http://www.copenhagendiagnosis.org/executive_summary.html

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Ocean Acidification  

• Oceans absorb much of the carbon dioxide (CO2) that humans emit, and as the gas dissolves in the oceans, it forms carbonic acid and increases the acidity (lowers the pH) of the ocean water. In October 2008, a panel of 155 scientists declared that ocean acidification threatens the world’s coral reefs, shellfish, and marine ecosystems generally. The panel concluded that “ocean acidification may render most regions chemically inhospitable to coral reefs” by 2050. http://ioc3.unesco.org/oanet/Symposium%202008/MonacoDeclaration.pdf 

• Increased acidity reduces the amount of carbonate in the oceans and makes it harder for shell-forming organisms to grow. This negatively impacts sea creatures such as corals and certain types of plankton that depend on the availability of carbonate to make their shells. Since many fisheries depend on corals and other shell-forming organisms to support their food chains, ocean acidification is a direct threat to food security, in addition to threatening biodiversity, tourism, and coastal protection (Hoegh-Guldberg et al. 2007). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• A decline in calcification rates (i.e., shell weights) has already been observed for several species (Moy et al. 2009; De'ath, Lough, and Fabricius 2009). Conditions detrimental to high-latitude marine ecosystems could develop within the next few decades (Orr et al. 2005). A recent modeling study concluded that by the time atmospheric concentrations of CO2 reach 560 ppm “all coral reefs will cease to grow and start to dissolve” (Silverman et al. 2009). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

Arctic Ice

• According to the IPCC’s Climate Change Synthesis Report, observed decreases in snow and ice extent are also consistent with warming. Satellite data since 1978 show that annual average Arctic sea ice extent has shrunk by 2.7 [2.1 to 3.3]% per decade, with larger decreases in summer of 7.4 [5.0 to 9.8]% per decade. Mountain glaciers and snow cover on average have declined in both hemispheres. The maximum areal extent of seasonally frozen ground has decreased by about 7% in the Northern Hemisphere since 1900, with decreases in spring of up to 15%. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Temperatures at the top of the permafrost layer have generally increased since the 1980s in the Arctic by up to 3°C. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• The Greenland Ice Sheet is losing mass and contributing to sea level rise. Satellite observations indicate that 2007 was a record year for Greenland surface melt—60 percent more melt than the previous record in 1998 (Mote 2007; Tedesco 2007). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• Increased melting along the edges of the Greenland Ice Sheet have exceeded annual snowfall in the interior regions (Mernild et al. 2009). Independent measurements from different satellites suggest that the Greenland Ice Sheet entered a period of accelerated melting starting in the summer of 2004 (Chen, Wilson, and Tapley 2006). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• The rate of ice melt in Greenland since 1990 and the significant increase in summer temperatures in Greenland have been linked directly to global warming (Hanna et al. 2008).

Arctic sea ice is melting more quickly than projected.

• Recent studies indicate that the Arctic will probably be free of sea ice during the summer sometime between 2030 and 2080, much earlier than previously anticipated (Boé et al. 2009; Wang and Overland 2009). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• The extent of Arctic sea ice at its summertime minimum has declined by 34 percent since 1979, reaching a new record low in 2007. The 2008 summertime sea ice extent was the second lowest on record, and 2008 may have set a new record for the lowest total volue of sea ice. http://www.arctic.noaa.gov/reportcard/seaice.html

• Models differ in their projections, but on average they underestimate by threefold the rate of sea ice loss that has been observed over the past three decades (Stroeve et al. 2007). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• Because ice is highly reflective, but open water absorbs most of the incoming sunlight, an ice-free Arctic would accelerate global warming. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

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Antarctic Ice

Antarctic ice shelves are collapsing more rapidly than expected.

• Ice shelves prevent rapid flow of land-based ice into the ocean by serving as a support structure. When ice shelves collapse, the glaciers behind them begin to flow into the ocean more rapidly, accelerating sea level rise (Rignot et al. 2004). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• The West Antarctic Ice Sheet continues to exhibit accelerated melting, with 10 major ice shelf collapses in the last decade. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• Most recently, the Wilkins Ice Shelf, along the West Antarctic Peninsula, suffered two large breaks: one in early 2008 andanother in April 2009, when an ice bridge connecting the icesheet to a small island collapsed. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

Improved analysis suggests that Antarctica is warming.

• A recent analysis indicates that West Antarctica has warmed at about the same rate as the rest of the globe over the past 50 years and that East Antarctica (and the continent as a whole) has also warmed slightly (Steig et al. 2009). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• Until recently, sparse data suggested that Antarctica—except for the Antarctic Peninsula—had cooled slightly over the past four decades (Chapman and Walsh 2007), but as noted in the AR4, models predict that Antarctica should be warming. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• The few long-term monitoring stations are mostly near the coasts, however, making it difficult to estimate the temperature trend for the entire continent. This new analysis provides better spatial understanding of temperature trends in Antarctica by combining the long-term records from a small number of older weather stations with the higher quality, short-term records from many more locations. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• Antarctica, on average, has warmed more slowly than the Arctic because (1) Antarctica is almost entirely covered by ice, which reflects sunlight back to space; (2) it is surrounded entirely by oceans, which warm more slowly than land; and (3) it lies under the stratospheric ozone hole, which has a regional cooling effect during the spring.http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

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Precipitation

• Trends from 1900 to 2005 have been observed in precipitation amount in many large regions. Over this period, precipitation increased significantly in eastern parts of North and South America, northern Europe and northern and central Asia whereas precipitation declined in the Sahel, the Mediterranean, southern Africa and parts of southern Asia. Globally, the area affected by drought has likely increased since the 1970s. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

Extreme Weather

Some extreme weather events have changed in frequency and/or intensity over the last 50 years:

• There is observational evidence of an increase in intense tropical cyclone activity in the North Atlantic since about 1970, and suggestions of increased intense tropical cyclone activity in some other regions where concerns over data quality are greater. Multi-decadal variability and the quality of the tropical cyclone records prior to routine satellite observations in about 1970 complicate the detection of long term trends in tropical cyclone activity. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• Average Northern Hemisphere temperatures during the second half of the 20th century were very likely higher than during any other 50-year period in the last 500 years and likely the highest in at least the past 1300 years. http://www.ipcc.ch/pdf/assessment-report/ar4/syr/ar4_syr.pdf

• For the regions of hurricane formation in the Atlantic and Pacific Oceans, new research finds a significant chance (84 percent) that human activities are responsible for most of the observed increase in the sea surface temperature, which contributes to more intense hurricanes (Santer et al. 2006). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

Permafrost

Permafrost is thawing more quickly than previously thought.

• Most of the Arctic land mass sits on permanently frozen soils (permafrost) that contain large amounts of carbon—significantly more than currently exists in the Earth’satmosphere (Zimov, Schuur, and Chapin III 2006; Ping et al.2008; Shuur et al. 2008). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• If these soils thaw, they will release large amounts of carbon into the atmosphere in the form of CO2 and CH4 (methane), the two most important greenhouse gases. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• The AR4 noted that permafrost temperatures have increased in many locations, but new research suggests that the permafrost may be thawing at a faster rate. Methane emissions from Siberian thaw lakes originate from thawing ancient organic matter below the surface. Methane emissions from these lakes may be more than five times higher than previous estimates, and expansion of thaw lakes in response to Arctic warming has led to an estimated 58 percent increase in methane emissions, largely from thawing permafrost (Walter et al. 2006). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• With further warming, methane emissions would increase further and perhaps nonlinearly, and since methane is a strong greenhouse gas, this process would amplify global warming. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• Many permafrost soils have warmed rapidly in recent decades, and the large amount of carbon in these soils “would release approximately 10 times the current atmospheric CH4 burden” (Walter, Smith, and Chapin III 2007). At present, however, scientists lack sufficient knowledge to predict how rapidly this process will accelerate. http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

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Irreversible Climate Change

• The impacts of climate change may persist for more than 1000 years, even after human-induced emissions of CO2 stop completely. New studies find that warmer temperatures and changes in precipitation caused by CO2 emissions from human activity are largely irreversible. Atmospheric temperatures are not expected to decrease for many centuries to millennia, even after human-induced greenhouse gas emissions stop completely (Matthews and Caldeira 2008; Solomon et al. 2009; Eby et al. 2009). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• In addition to long-term increases in temperature, climate models also suggest that a peak in CO2 levels between 450 and 600 ppm produces irreversible rainfall reductions in many parts of the world. For example, a 15-20 percent reduction in rainfall in the southwestern United States is predicted—a larger decrease than the “Dust Bowl” of the 1930s (Solomon et al. 2009). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

• In the models, these changes persist for more than 1000 years for two reasons: (1) the long lifetime of CO2 in the atmosphere—some 25 percent of it may remain in the atmosphere for more than 5000 years (Montenegro et al. 2007; Eby et al. 2009)—and (2) the long period of time required for the transfer of heat between the oceans and the atmosphere. The uptake of heat by the oceans is expected to slow, causing atmospheric temperatures to remain elevated for thousands of years (Eby et al. 2009;Solomon et al. 2009). http://www.pewclimate.org/docUploads/Key-Scientific-Developments-Since-IPCC-4th-Assessment.pdf

Tipping Points

Delay in action risks irreversible damage:

• Several vulnerable elements in the climate system (e.g. continental ice sheets, Amazon rainforest, West African monsoon and others) could be pushed towards abrupt or irreversible change if warming continues in a business-as-usual way throughout this century. The risk of transgressing critical thresholds ('tipping points') increase strongly with ongoing climate change. Thus waiting for higher levels of scientific certainty could mean that some tipping points will be crossed before they are recognized. http://www.copenhagendiagnosis.org/executive_summary.html

• If global warming is to be limited to a maximum of 2ºC above pre-industrial values, global emissions would have to peak between 2015 and 2020 and then decline rapidly. http://www.copenhagendiagnosis.org/executive_summary.html

• To stabilize climate, a de-carbonized global society – with near-zero emissions of CO2 and other long-lived greenhouse gases – will have to be reached well within this century. More specifically, the average annual per-capita emissions will have to shrink to well under 1 metric ton CO2 by 2050. This is 80-95% below the per-capita emissions in developed nations in 2000. http://www.copenhagendiagnosis.org/executive_summary.html

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About the Sources 

In 2007, the Intergovernmental Panel of Climate Change (IPCC) released its Climate Change Synthesis Report, an integrated view of climate change as the final part of the IPCC’s Fourth Assessment Report (AR4).The report is based on the assessment carried out by the three Working Groups (WGs) of the Intergovernmental Panel on Climate Change (IPCC) up to July 2006.

Since July 2006, a significant body of new peer-reviewed science has been published and synthesized, in June 2009, by the Pew Center of Global Climate Change, and the Copenhagen Diagnosis: Climate Science Report.

Other sources include: NOAA Earth System Research Laboratory, NASA Goddard Institute for Space Studies (GISS) Surface Temperature Analysis, NOAA National Climatic Data Center