Science

IPCC Fourth Assessment Report, Working Group II

IPCC AR4 WGII: "Impacts, Adaptation & Vulnerability"

The second installment to the IPCC Fourth Assessment Report was released April 6, 2007. The Working Group II installment to the report addresses "Impacts, Adaptation and Vulnerability". The WGII report provides a detailed analysis of observed changes in natural and human systems and the relationship between those observed changes and climate change, as well as a detailed assessment of projected future vulnerability, impacts, and response measures to adapt to climatic changes for main sectors and regions.

According to the IPCC, the report from Working Group II on the impacts of climate change answers the following questions:

  • What is the current state of knowledge on impacts of climate change?
  • What is the state of knowledge on impacts under different levels of adaptation?
  • What are the impacts under different levels of mitigation?
  • What is the state of knowledge concerning observed effects?

For the full report, visit the IPCC website. For a summary of the report, click here (pdf).

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IPCC Fourth Assessment Report, Working Group I

IPCC AR4 WGI: "The Physical Science of Climate Change"

The first installment to the IPCC Fourth Assessment Report was released February 2, 2007. According to the IPCC, the Working Group I Report, "The Physical Science Basis", assesses the current state of knowledge about the natural and human drivers of climate change, reflecting the progress of the climate change science in the observation of the atmosphere, the Earth's surface and oceans. It provides a paleoclimatic perspective and evaluates the Earth's surface and oceans. Main topics include changes in atmospheric composition, observation of various climate parameters, coupling between changes in climate and biogeochemistry, evaluation of models and attribution of climate change.

Working Group I Report, "The physical science basis", assesses the current state of knowledge about the natural and human drivers of climate change, reflecting the progress of the climate change science in the observation of the atmosphere, the Earth's surface and oceans. It provides a paleoclimatic perspective and evaluates future projections of climate change. Main topics include changes in atmospheric composition, observation of various climate parameters, coupling between changes in climate and biogeochemistry, evaluation of models and attribution of climate change..

According to the IPCC, the report from Working Group I on the science of climate change answers the following questions:

  • What progress has been made in understanding and attributing climate change?
  • What do observations of the atmosphere, oceans, sea level, snow and ice tell us?
  • How has climate been behaving in the last hundreds of thousands of years?
  • Which are the projections of future changes?

For the full report, visit the IPCC website. For a summary of the report, click here (pdf). Relevant materials, including a statement from C2ES can be linked to from the "Related Content" box above.

Back to coverage of the IPCC's Fourth Assessment Report

Statement: IPCC Fourth Assessment Report, Working Group II

Intergovernmental Panel on Climate Change (IPCC) Releases New Assessment Report on the Impacts of Climate Change

Statement by the Pew Center on Global Climate Change

April 6, 2007

The IPCC Fourth Assessment “Summary for Policymakers” Working Group II report represents the IPCC’s strongest statement to date on the impacts of global climate change. Because of a dramatic increase in the number and quality of observations, this report concludes that, “it is likely [better than 2:1 odds] that anthropogenic warming has had a discernible influence on many physical and biological systems.” The report also projects with greater confidence than in the past that many regions, including North America, will experience severe impacts in the future, even for moderate warming scenarios. Particularly vulnerable are low-lying coastal regions worldwide. Many poor countries at low latitudes are also particularly vulnerable because of a combination of strong climate impacts, low capacity for adaptation, and heavy reliance on climate-impacted resources, such as local food and water supplies.

The assessment is based on extensive published, peer-reviewed scientific literature.  Today’s report is the second of three major studies that comprise the Fourth Assessment with input from more than 1,200 authors and 2,500 scientific expert reviewers from more than 130 countries. The first report, released in February 2007, examined the physical science basis for climate change. The third report, to be released in May 2007, will explore the solutions to global climate change, particularly options for reducing greenhouse gas emissions.

 

Statement by Eileen Claussen, President Pew Center on Global Climate Change

April 6, 2007

This week began with a landmark decision by the US Supreme Court and ended with the release of the IPCC's 4th Assessment on climate change impacts.  Following the Supreme Court's decision, it's clear that EPA has the authority – and should -- regulate CO2, and the IPCC report delivered the strongest statement to date on the consequences of climate change. Taken together with increasing calls from CEOs, states, and the public, the message is loud and clear: Read our lips - We need mandatory climate policy in the United States. 

 

Trends in CO2 Emissions

This figure shows emissions of carbon dioxide (CO2) by fuel source across all sectors of the economy. The fuels shown are coal, natural gas, petroleum, as well as the total emissions.

Overall, coal and petroleum consumption are down since 2007, while natural gas use has increased. In the electric power sector, natural gas, which emits about half the amount of CO2 as coal, is being used more extensively due to its lower price. In the transportation sector, petroleum consumption is down due to an increase in car and light truck fuel economy (for a similar number of vehicle miles traveled, year-on-year). Correspondingly, total emissions have declined since 2007. 

Source: EIA (2012)

U.S. CO2 Emissions from the Electric Power Sector

This figure shows the emissions of carbon dioxide (CO2) from the burning of fossil fuels for electric power generation. The electricity-generating fuels shown here are coal, natural gas, petroleum and non-biomass waste. Natural gas, which emits about half the amount of CO2 as coal, is being used more extensively due to its lower price and displacing coal-fired generation, while petroleum-fired electricity generation continues to be retired.

Source: EIA (2012)

U.S. Trends in Greenhouse Gas Emissions

This figure shows the trend in U.S. greenhouse gas emissions between 1990 and 2010. Emissions increased by 10.5 percent between 1990 and 2010.

Greenhouse gas emissions declined in 2008 and 2009 for two main reasons:

  1. A larger share of electricity was generated with natural gas (and to a much lesser extent renewable energy). This offset coal-fired electricity generation, which emits about two times the amount of carbon dioxide (a greenhouse gas) as natural gas-fired electricity generation per unit of electric energy.
  2. Economic activity decreased during the Great Recession, which ran from December 2007 until June 2009.

Emissions increased 3.1 percent from 2009 to 2010, as economic growth returned to the United States.


 
Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2010 (EPA 2012)


 

Greenhouse Gas Emissions by Sector

In 2010, the United States emitted over 6.8 billion metric tons of greenhouse gases (CO2e). Greenhouse gases are emitted by all sectors of the economy, including electric power (34% of total), transportation (27%), industry (21%), residential & commercial (11%), and agriculture (7%).  


 
Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2010 (EPA 2012)

U.S. Greenhouse Gas Emissions by Gas

In 2010, the United States emitted over 6.8 billion metric tons of greenhouse gases (CO2e). Carbon dioxide accounted for the largest percentage of greenhouse gases (84%), followed by methane (10%), nitrous oxide (4%), and other greenhouse gases (2%). Total U.S. emissions for 2010 totaled 6,821 million metric tons of CO2e and net emissions, taking sinks into account, totaled 5,747 tons CO2e.


Source: Inventory of U.S. Greenhouse Gas Emissions and Sinks 1990-2010 (EPA 2012)

Congressional Briefing Series on Science and Impacts: Sea Level Rise

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Sea level rise is one of the most widespread climate impacts expected to result from human-induced global warming. New evidence from modern satellite observations on the one hand, and from the study of how large polar ice sheets responded to ancient global warming events on the other, suggests that global warming is already causing sea level to rise and that it could rise faster and to a greater extent this century—and beyond—than previously estimated. This briefing will help congressional staff understand recent scientific progress and current scientific thought on sea level rise.

Friday February 9, 2007
10:00-11:30 AM
2325 Rayburn House Office Building

 

Sea level rise is one of the most widespread climate impacts expected to result from human-induced global warming. New evidence from modern satellite observations on the one hand, and from the study of how large polar ice sheets responded to ancient global warming events on the other, suggests that global warming is already causing sea level to rise and that it could rise faster and to a greater extent this century—and beyond—than previously estimated. This briefing will help congressional staff understand recent scientific progress and current scientific thought on sea level rise.

Following a brief introduction to global climate change by Dr. Jay Gulledge, two leading sea level experts, Dr. Steve Nerem and Dr. Jonathan Overpeck, will describe the present state of the science on global sea level rise, with emphasis on state-of-the-art satellite measurements of contemporary sea level change, the various climate processes that contribute to sea level rise, and lessons learned from studying ancient climate–sea level relationships. Following short scientific presentations from each scientist, there will be ample time for the audience to interact directly with these internationally recognized experts.

 


R. Steven Nerem, Ph.D.
University of Colorado
Dr. Steve Nerem is Professor of Aerospace Engineering Sciences at the University of Colorado at Boulder and a fellow of the Cooperative Institute for Research in Environmental Sciences. Prior to joining the CU faculty in 2000, he was Assistant Professor and then Associate Professor of Aerospace Engineering for four years at the University of Texas at Austin. Prior to that he was a geophysicist with NASA/Goddard Space Flight Center for six years. He earned his Ph.D. in Aerospace Engineering from The University of Texas at Austin. Dr. Nerem has authored approximately 60 peer-reviewed journal publications covering a variety of topics related to his specialty, which involves satellite orbit determination, remote sensing, and measuring the Earth's shape, gravity field, and sea level from space. He is a Contributing Author for the 2007 Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Dr. Nerem has received more than a dozen awards for his work, including NASA's Exceptional Scientific Achievement Medal for his research in the area of gravity field determination.

Jonathan T. Overpeck, Ph.D.
University of Arizona
Dr. Overpeck is Director of the Institute for the Study of Planet Earth and professor of Geosciences at the University of Arizona, Tucson. Prior to joining the faculty in 1999 he was head of the NOAA Paleoclimatology Program at the National Geophysical Data Center in Boulder, Colorado for nine years. He earned a Ph.D. in geological sciences from Brown University. Dr. Overpeck has authored over 100 papers that focus on global change dynamics, with a major focus on how and why climate systems vary on timescales of decades and longer. Current work focuses on the Asian and West African Monsoon systems, tropical Atlantic variability, El Niño-Southern Oscillation dynamics, Arctic environmental change, and reconstruction of ancient environments. He is a Coordinating Lead Author for the 2007 Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Dr. Overpeck has received numerous awards recognizing his climate research, including the U.S. Department of Commerce Gold Medal and the American Meteorological Society Walter Orr Roberts Award.

Jay Gulledge, Ph.D.
Pew Center on Global Climate Change
Dr. Gulledge is Senior Research Fellow for Science and Impacts at the Pew Center on Global Climate Change. He serves as the Center’s in-house scientist and coordinates its work to communicate the state of knowledge on the science and environmental impacts of global climate change to policy-makers and the public. He is also an adjunct Associate Professor at the University of Wyoming, home to his academic research on biological cycling of atmospheric greenhouse gases, which he publishes regularly in peer-reviewed journals. Prior to joining the Pew Center, he served on the faculties of Tulane University and University of Louisville. Dr. Gulledge earned a PhD in ecosystem sciences from the University of Alaska Fairbanks. He currently serves as an associate editor of Ecological Applications, a peer-reviewed journal published by the Ecological Society of America.

Sea Level Rise - The State of the Science

Outline:

Click here for an extended version plus references (pdf)


General Background

  • Two primary processes contribute to sea level rise (SLR):
  1. Thermal expansion—the increase in water volume resulting from heat uptake;
  2. Mass inputs—the transfer of freshwater from land to the ocean. Large ice sheets on Greenland and Antarctica represent the largest potential source of additional water mass (#2 below).
  • There are two general mechanisms by which such ice sheets transfer water to the ocean:
  1. Surface melting of ice on land with subsequent runoff into the ocean;
  2. Ice dynamics, wherein ice actually flows from land into the ocean
  • New evidence indicates that ice flow is accelerating around Greenland and Antarctica, making this process the greatest source of uncertainty for predicting future SLR as warming proceeds.

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Ancient Sea Level Change

  • Over the past four cycles, each lasting about 100,000 years, sea level rose and fell by about 400 feet, with ice ages having lower sea level and warm interglacial periods having higher sea level. Contributions from land-based ice sheets dominated SLR during interglacial warming.
     
  • During the warmest part of the last interglacial period (about 130,000 years ago), global average temperature was 2-3 °F warmer than today and global sea level was 13-20 feet higher. During the Middle Pliocene (3 million years ago), global temperature was 3.5-5.5 °F warmer than today and sea level was 80-115 feet higher.
     
  • If emissions of man-made greenhouse gases continue without abatement, the earth could warm by 5.5 °F (3 °C) within the next century.
     
  • The complete loss of large ice sheets would take from several centuries to millennia, but warming could cross a threshold within decades that could permanently destabilize large ice sheets.

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Recent Sea Level Rise

  • Based on tide gauges, sea level rose by an average of 0.7 inches per decade and accelerated by 0.05 inches per decade over the 20th century.
     
  • More accurate satellite measurements indicate that global sea level has risen by 1.2 inches over the past decade, about 70% faster than the 20th century average.
     
  • Scientists assumed that thermal expansion dominated contemporary SLR, but recent progress reveals that freshwater contributions from land dominate, consistent with recent acceleration of ice loss from glaciers.

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Projections of Future SLR

  • Because the ocean has an enormous thermal inertia, it takes many decades for sea level to adjust to a quantity of heat that it absorbs. This delay means that even if man-made greenhouse gas emissions were halted today, sea level rise would be committed to an additional 0.4-1.0 foot by the end of this century.
     
  • In 2001 the Third Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) projected that sea level would rise by 0.3-2.9 feet by the end of the 21st century.
     
  • In 2007 the Fourth Assessment Report of the IPCC projected that sea level would rise by 0.6-1.9 feet by the end of the 21st century.
     
  • The lower ends of the projected SLR ranges from the Third and Fourth IPCC reports are similar to the sea level rise commitment described above, leaving little or no room for additional SLR generated by continued greenhouse gas emissions. The upper end of both omits the uncertainty associated with the future ice dynamical changes in Greenland and West Antarctica.
     
  • Current SLR models undershoot the sea level change observed during the 20th century, possibly because they do not adequately simulate freshwater mass contributions from land. As an alternative, a recent study extended the statistical relationship between temperature rise and SLR observed during the 20th century, using models of future temperature change to drive SLR. This empirical approach estimated 21st century SLR to be in the range of 1.6-4.5 feet, if manmade greenhouse gas emissions continue to grow.

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Summary

  • Both long-term tide gauge measurements and recent satellite measurements suggest that SLR accelerated during the 20th century, concomitant with increasing global temperature.
     
  • One of the most significant developments of recent years is the realization that mass contributions from land ice have dominated contemporary SLR.
     
  • Large polar ice sheets are more sensitive to surface warming than previously realized, and large dynamical changes are now being observed on the Greenland and West Antarctic ice sheets.
     
  • New understanding of how these ice sheets behaved in the past suggests that they could add water mass to the oceans much more quickly than previously assumed.
     
  • The Fourth Assessment Report of the IPCC projects a 21st century sea level rise of 0.6-1.9 feet by 2100, but notes that accelerated glacial melt could contribute another 0.7 feet, raising the upper end to 2.6 feet.
     
  • A new empirical projection of SLR for the 21st century indicates that sea level could rise by 1.6-4.5 feet this century.
     
  • The potential for the rapid collapse of large ice sheets seems more plausible than in the recent past, and some scientists therefore warn that continued anthropogenic warming could result in the triggering of abrupt sea level rise within the current century.

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