Key Conclusions from the 2009 Reports

Summarized here are 18 statements from two recent scientific reports on global warming and climate change.  The reports are:

Global Climate Change Impacts in the United States (2009)

Presenting the latest scientific consensus report on U.S. climate change impacts, this report by the U.S. Global Change Research Program presents inter-agency findings by a long list of experts enlisted by the U.S. Government (cited here as “US Impacts, 2009”).  All quotes below from this report are from “Key Findings,” pg. 12.

Copenhagen Diagnosis Updating the Latest Global Climate Science (2009)

This was written for policy-makers, stakeholders, the media and the broader public to synthesize the most policy-relevant climate science.  It relies on the 100s of papers published since the editorial cut-off for the Nobel-Prizing-Winning “Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) (2007).”  All quotes below from this report are from the “Executive Summary,” (cited here as “Copenhagen Diagnosis 2009”).


18 Key Conclusions

Click on topics below to view specific subjects or scroll down to read them all.

Evidence for Climate Change Is Beyond Reasonable Doubt

1.  Global Warming is Unequivocal and Primarily Human-Induced.

“Global temperature has increased over the past 50 years.  This observed increase is due primarily to human induced emissions of heat-trapping gases.”  (US Impacts, 2009)

2.  Recent global temperatures demonstrate human-induced warming. 

“Over the past 25 years temperatures have increased at a rate of 0.19°C per decade, in very good agreement with predictions based on greenhouse gas increases. Even over the past ten years, despite a decrease in solar forcing, the trend continues to be one of warming. Natural, short-term fluctuations are occurring as usual, but there have been no significant changes in the underlying warming trend.”  (Copenhagen Diagnosis 2009)

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Climate Change Already Underway and Projected to Grow

3.  Surging greenhouse gas emissions. 

“Global carbon dioxide emissions from fossil fuels in 2008 were 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 2°C, even with zero emissions after 2030. Every year of delayed action increases the chances of exceeding 2°C warming.”  (Copenhagen Diagnosis 2009)

4.  Widespread climate-related impacts are occurring now and are expected to increase. 

“Climate-related changes are already observed in the United States and its coastal waters.  These include increases in heavy downpours, rising temperature and sea level, rapidly retreating glaciers, thawing permafrost, lengthening growing seasons, longer ice-free seasons in the ocean and on lakes and rivers, earlier snowmelt, and alterations in river flows. These changes are projected to grow.” (US Impacts, 2009) 

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Climate Change Impacts on Ice Sheets and Rising Sea Levels

5.  Acceleration of melting ice-sheets, glaciers and ice-caps.  

“A wide array of satellite and ice measurements now demonstrate beyond doubt that both the Greenland and Antarctic ice-sheets are losing mass at an increasing rate. Melting of glaciers and ice-caps in other parts of the world has also accelerated since 1990.”  (Copenhagen Diagnosis 2009)

6.  Rapid Arctic sea-ice decline

“Summer-time melting of Arctic sea-ice has accelerated far beyond the expectations of climate models. The area of summertime sea-ice melt during 2007-2009 was about 40% less than the average prediction from IPCC AR4 climate models.” (Copenhagen Diagnosis 2009) 

7.  Current sea-level rise underestimated.  

“Satellites show recent 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.”  (Copenhagen Diagnosis 2009)

8.  Sea-level predictions revised.  

“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.” (Copenhagen Diagnosis 2009)

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Climate Change Impacts on Water, Food, Health, Energy – and More

9.  Widespread climate-related impacts are occurring now and are expected to increase.  

“Climate changes are already affecting water, energy, transportation, agriculture, ecosystems, and health. These impacts are different from region to region and will grow under projected climate change.”  (US Impacts, 2009)

10.  Climate change will stress water resources.

“Water is an issue in every region, but the nature of the potential impacts varies. Drought, related to reduced precipitation, increased evaporation, and increased water loss from plants, is an important issue in many regions, especially in the West. Floods and water quality problems are likely to be amplified by climate change in most regions. Declines in mountain snowpack are important in the West and Alaska where snowpack provides vital natural water storage.” (US Impacts, 2009)

11.  Crop and livestock production will be increasingly challenged.

“Many crops show positive responses to elevated carbon dioxide and low levels of warming, but higher levels of warming often negatively affect growth and yields. Increased pests, water stress, diseases, and weather extremes will pose adaptation challenges for crop and livestock production.”  (US Impacts, 2009)

12.  Risks to human health will increase.

Harmful health impacts of climate change are related to increasing heat stress, waterborne diseases, poor air quality, extreme weather events, and diseases transmitted by insects and rodents. Reduced cold stress provides some benefits.  Robust public health infrastructure can reduce the potential for negative impacts.”  (US Impacts, 2009)

13.  Climate change will interact with many social and environmental stresses. 

Then we should quote accurately rather than make it up.“Climate change will combine with pollution, population growth, overuse of resources, urbanization, and other social, economic, and environmental stresses to create larger impacts than from any of these stresses alone.” (US Impacts, 2009) 

14.  Coastal areas are at increasing risk from sea level rise and storm surge.

“Sea-level rise and storm surge place many U.S. coastal areas at increasing risk of erosion and flooding, especially along the Atlantic and Gulf Coasts, Pacific Islands, and parts of Alaska. Energy and transportation infrastructure and other property in coastal areas are very likely to be adversely affected.”  (US Impacts, 2009)

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Irreversible Damage Risked by Delayed Action

15.  Thresholds will be crossed leading to large changes in climate and ecosystems.

“There are a variety of thresholds in the climate system and ecosystems. These thresholds determine, for example, the presence of sea ice and permafrost, and the survival of species, from fish to insect pests, with implications for society. With further climate change, the crossing of additional thresholds is expected.”  (US Impacts, 2009)

16.  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”) increases 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.”  (Copenhagen Diagnosis 2009).

17.  The turning point must come soon.  

“If global warming is to be limited to a maximum of 2 °C above pre-industrial values, global emissions need to peak between 2015 and 2020 and then decline rapidly. To stabilize climate, a decarbonized global society – with near-zero emissions of CO2 and other long-lived greenhouse gases – needs 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.”  (Copenhagen Diagnosis 2009)•

18.  Future climate change and its impacts depend on choices made today.  

“The amount and rate of future climate change depend primarily on current and future human-caused emissions of heat-trapping gases and airborne particles. Responses involve reducing emissions to limit future warming, and adapting to the changes that are unavoidable.”  (US Impacts, 2009)

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(All quotes below from this report are from “Key Findings,” pg. 12)


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