Climate Change Science Program: Difference between revisions

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The '''Climate Change Science Program''' ('''CCSP''') was the program responsible for coordinating and integrating research on [[global warming]] by U.S. government agencies from February 2002 to June 2009.<ref>[http://www.climatescience.gov/infosheets/factsheet1/default.htm Climate Change Science Program] {{webarchive|url=https://web.archive.org/web/20070207092833/http://www.climatescience.gov/infosheets/factsheet1/default.htm |date=2007-02-07 }} 2006. Overview of the U.S. Climate Change Science Program, Fact Sheet 1. Washington, D.C.DC (January)</ref> Toward the end of that period, CCSP issued 21 separate climate assessment reports that addressed [[Climate Change Science Program#Observations and causes of climate change|climate observations]], changes in the atmosphere, expected climate change, [[Climate Change Science Program#Impacts and adaptation|impacts and adaptation]], and risk management issues. Shortly after President Obama took office, the program's name was changed to U.S. [[Global Change Research Program]] (USGCRP) which was also the program's name before 2002. Nevertheless, the [[Obama Administration]] generally embraced the CCSP products as sound science providing a basis for climate policy.<ref>See [[Climate Change Science Program#Global Climate Change Impacts in the United States|Global Climate Change Impacts in the United States]].</ref> Because those reports were mostly issued after the [[IPCC Fourth Assessment Report|Fourth Assessment Report]] of the [[Intergovernmental Panel on Climate Change]] (IPCC), and in some cases focused specifically on the United States, they were generally viewed within the United States as having an importance and scientific credibility comparable to the IPCC assessments for the first few years of the Obama Administration.<ref>For example, see [http://epa.gov/climatechange/endangerment/downloads/Endangerment%20TSD.pdf Endangerment and Cause or Contribute Findings for Greenhouse Gases under Section 202(a) of the Clean Air Act: Technical Support Document] 2009. U.S. Environmental Protection Agency. Washington, D.C.DC (December)</ref>

==The products==

The primary outputs from the CCSP were its strategic plan and 21 Synthesis and Assessment Products (SAP), five of which were released on January 16, 2009, the last business day of the Bush Administration.<ref>[http://www.climatescience.gov/Library/sap/sap-summary.php Climate Change Science Program] {{webarchive|url=https://web.archive.org/web/20070819232331/http://www.climatescience.gov/Library/sap/sap-summary.php |date=2007-08-19 }} 2009. Information on Synthesis and Assessment Products</ref> The CCSP Strategic Plan of 2003<ref>[http://www.climatescience.gov/Library/stratplan2003/default.htm U.S. Climate Change Science Program] {{webarchive|url=https://web.archive.org/web/20070215085829/http://www.climatescience.gov/Library/stratplan2003/default.htm |date=2007-02-15 }}, 2003. Strategic Plan for the U.S. Climate Change Science Program. Washington, D.CDC. See also [http://www.climatescience.gov/Library/pressreleases/pressrelease24jul2003.htm Press release of 24 July 2003] {{webarchive|url=https://web.archive.org/web/20070203080618/http://www.climatescience.gov/Library/pressreleases/pressrelease24jul2003.htm |date=3 February 2007 }}</ref> defined five goals:

# Extend knowledge of the Earth’s past and present climate and environment, including its natural variability, and improve understanding of the causes of observed changes (see [[Climate Change Science Program#Observations and causes of climate change|Observations and causes of climate change]]),

# Improve understanding of the forces bringing about changes in the Earth’s climate and related systems (see [[Climate Change Science Program#Changes in the atmosphere|Changes in the atmosphere]])

# Reduce uncertainty in projections of how the Earth’s climate and environmental systems may change in the future (see [[Climate Change Science Program#Climate projections|Climate projections]])

# Understand the sensitivity and adaptability of different natural and managed systems to climate and associated global changes (see [[Climate Change Science Program#Impacts and adaptation|Impacts and adaptation]])

# Explore the uses and identify the limits of evolving knowledge to manage risks and opportunities related to climate variability and change (see [[Climate Change Science Program#Using information to manage risks|Using information to manage risks]])

The plan also proposed 21 SAP's, each of which were designed to support one of these five goals. The plan was updated in 2008.<ref>[http://www.climatescience.gov/Library/stratplan2008/ Climate Change Science Program.] {{webarchive|url=https://web.archive.org/web/20090513010457/http://www.climatescience.gov/Library/stratplan2008/ |date=2009-05-13 }} 2008 Revised Research Plan for the U.S. Climate Change Science Program. Washington, D.C.DC</ref>

The following sections discuss the SAP's, grouped according to the five topic areas.

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====The Arctic and other high latitude areas (SAP 1.2)====

On January 16, 2009 (the last business day of the Bush Administration), USGS released ''Past Climate Variability and Change in the Arctic and at High Latitudes''.<ref>[http://www.climatescience.gov/Library/sap/sap1-2/default.php CCSP, 2009.] {{webarchive|url=https://web.archive.org/web/20090706025403/http://www.climatescience.gov/Library/sap/sap1-2/default.php |date=2009-07-06 }} Past Climate Variability and Change in the Arctic and at High Latitudes. Alley R.B., Brigham-Grette J., Miller G.H., Polyak L., and White J.W.C. U.S. Geological Survey, Washington D.C., USADC. 270 pp.</ref> According to the USGS press release,<ref>[http://www.usgs.gov/newsroom/article.asp?ID=2109&from=rss_home U.S. Geological Survey, Office of Communication] Arctic Heats Up More than Other Places, January 16, 2009</ref> the report shows that:

* The Arctic has recently been warming about as rapidly as it has ever warned throughout the entire record of past Arctic climate.

* The loss of sea ice during summers over the last few decades is highly unusual compared to the last few thousand years. Changes in Earth's orbit alone would have increased summer sea ice.

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====Scenarios of greenhouse gas emissions and atmospheric concentrations (SAP 2.1)====

The [[US Department of Energy]] released the second SAP in July 2007, entitled ''Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations and Review of Integrated Scenario Development and Application''.<ref>[http://www.climatescience.gov/Library/sap/sap2-1/default.php CCSP SAP 2.1 web page] {{webarchive|url=https://web.archive.org/web/20070205034037/http://www.climatescience.gov/Library/sap/sap2-1/default.php |date=2007-02-05 }} Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations and Review of Integrated Scenario Development and Application</ref> This two-volume report explored emission scenarios that could stabilize the [[radiative forcing|net effect]] of [[greenhouse gases]] at four different levels. It also outlined key principles and approaches for developing global change scenarios. The two reports were each written by a subset of the members of the Climate Change Science Program Product Development Advisory Committee, a panel organized under the [[Federal Advisory Committee Act]].<ref>[http://www.climatescience.gov/Library/sap/sap2-1/finalreport/sap2-1a-final-all.pdf CCSP 2007] {{webarchive|url=https://web.archive.org/web/20100527213938/http://www.climatescience.gov/Library/sap/sap2-1/finalreport/sap2-1a-final-all.pdf |date=2010-05-27 }}. Scenarios of Greenhouse Gas Emissions and Atmospheric Concentrations and Review of Integrated Scenario Development and Application. Washington, DDC.C.: United States Department of Energy</ref>

The report's executive summary stated that the emission reductions necessary to stabilize radiative climate forcing would "require a transformation of the global energy system, including reductions in the demand for energy... and changes in the mix of energy technologies and fuels." But the authors found great uncertainty in the price that would be necessary to stabilize climate forcing—as well as the resulting economic cost: " These differences are illustrative of some of the unavoidable uncertainties in long-term scenarios."

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====Other synthesis and assessment products====

In addition to SAP 2.1, CCSP produced three other reports to further the goal of improving quantification of climate forcing:

* NOAA released "North American Carbon Budget and Implications for the Global Carbon Cycle"<ref>[http://www.climatescience.gov/Library/sap/sap2-2/default.php CCSP 2007.] {{webarchive|url=https://archive.is/20120805114554/http://www.climatescience.gov/Library/sap/sap2-2/default.php |date=2012-08-05 }} The First State of the Carbon Cycle Report (SOCCR): The North American Carbon Budget and Implications for the Global Carbon Cycle. King, A.W., L. Dilling, G.P. Zimmerman, D.M. Fairman, R.A. Houghton, G. Marland, A.Z. Rose, and T.J. Wilbanks (editors). National Climatic Data Center, Asheville, NC, USA, 242 pp.</ref> (SAP 2.2) in November 2007.

* NASA released "Atmospheric Aerosol Properties and Climate Impacts"<ref>[http://www.climatescience.gov/Library/sap/sap2-3/default.php CCSP 2009] {{webarchive|url=https://web.archive.org/web/20090507192221/http://www.climatescience.gov/Library/sap/sap2-3/default.php |date=2009-05-07 }} Atmospheric Aerosol Properties and Climate Impacts. Mian Chin, Ralph A. Kahn, and Stephen E. Schwartz (editors). National Aeronautics and Space Administration, Washington, D.C., USADC. 128 pp.</ref> (SAP 2.3) on January 16, 2009.

* NOAA released "Trends in Emissions of Ozone-Depleting Substances, Ozone Layer Recovery, and Implications for Ultraviolet Radiation Exposure"<ref>[http://www.climatescience.gov/Library/sap/sap2-4/default.php CCSP, 2008] {{webarchive|url=https://web.archive.org/web/20090706024633/http://www.climatescience.gov/Library/sap/sap2-4/default.php |date=2009-07-06 }} Trends in Emissions of Ozone-Depleting Substances, Ozone Layer Recovery, and Implications for Ultraviolet

Radiation Exposure. Ravishankara, A.R., M.J. Kurylo, and C.A. Ennis (editors). National Climatic Data Center, Asheville, NC, 240 pp.</ref> (SAP 2.4) in November 2008.

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===Climate projections===

As provided in the CCSP strategic plan, four SAP's examined issues under CCSP's Goal 3:

* DOE released "Climate Models: An Assessment of Strengths and Limitations."<ref>[http://www.climatescience.gov/Library/sap/sap3-1/default.php CCSP 2008.] {{webarchive|url=https://web.archive.org/web/20070812000134/http://www.climatescience.gov/Library/sap/sap3-1/default.php |date=2007-08-12 }} Climate Models: An Assessment of Strengths and Limitations. Bader, D.C.DC, Covey, C., Gutowski, W.J., Held, I.M., Kunkel, K.E., Miller, R.L, Tokmakian, R.T., and Zhang, M.H. U.S. Department of Energy, Washington, DC, USA. 124 pp.]</ref> (SAP 3.1) in July 2008.

* NOAA released "Climate Projections Based on Emissions Scenarios for Long-Lived and Short-Lived Radiatively Active Gases and Aerosols."<ref>[http://www.climatescience.gov/Library/sap/sap3-2/default.php CCSP, 2008] {{webarchive|url=https://web.archive.org/web/20070423160211/http://www.climatescience.gov/Library/sap/sap3-2/default.php |date=2007-04-23 }} Climate Projections Based on Emissions Scenarios for Long-Lived and Short-Lived Radiatively Active Gases and Aerosols. H. Levy II, D.T. Shindell, A. Gilliland, M.D. Schwarzkopf, and L.W. Horowitz, (editor). National Climatic Data Center, Asheville, NC, USA, 100 pp.</ref> (SAP 3.2) in September 2008.

* NOAA released "Weather and Climate Extremes in a Changing Climate Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands."<ref>[http://www.climatescience.gov/Library/sap/sap3-3/default.php CCSP, 2008. ] {{webarchive|url=https://web.archive.org/web/20070423160111/http://www.climatescience.gov/Library/sap/sap3-3/default.php |date=2007-04-23 }} Climate Projections Based on Emissions Scenarios for Long-Lived and Short-Lived Radiatively Active Gases and Aerosols. H. Levy II, D.T. Shindell, A. Gilliland, M.D. Schwarzkopf, L.W. Horowitz, (editors). National Climatic Data Center, Washington, DDC.C., USA, 100 pp.</ref> (SAP 3.3) in June 2008.

* USGS released "Abrupt Climate Change."<ref>[http://www.climatescience.gov/Library/sap/sap3-4/default.php CCSP, 2008] {{webarchive|url=https://web.archive.org/web/20090507192340/http://www.climatescience.gov/Library/sap/sap3-4/default.php |date=2009-05-07 }} Abrupt Climate Change. Clark, P.U., A.J. Weaver (coordinating lead authors). U.S. Geological Survey, Reston, VA, 459 pp.</ref> (SAP 3.4) in December 2008.

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A committee set up under the [[Federal Advisory Committee Act]] monitored the progress of SAP 4.1, and questioned several aspects of the final report. The original plan included maps and estimates of wetland loss from a then-ongoing EPA mapping study conducted by James G. Titus,<ref>

{{Cite journal| author=Cornelia Dean | title=Next Victim of Warming: The Beaches | url=https://query.nytimes.com/gst/fullpage.html?res=9E0DE6DC1E31F933A15755C0A9609C8B63 | accessdate=15 June 2010 | journal=New York Times | date=June 20, 2006 }}</ref> who was also a lead author of SAP 4.1. Early drafts included the maps and results, but the final draft did not. Experts and environmental organizations objected to the deletions. The federal advisory committee also took issue with the maps' removal from SAP 4.1 and recommended that EPA publish the mapping study.<ref>[http://www.epa.gov/climatechange/effects/coastal/CESLAC.pdf Report of the Coastal Elevations and Sea Level Rise Advisory Committee] Report to the Administrator of the U.S. Environmental Protection Agency, October 2008.</ref> EPA later confirmed that EPA management had altered the report and suppressed the mapping study, although it declined to explain why.<ref>

{{Cite journal| author=Josh Harkinson and Kate Sheppard | title=Coastal Collapse | url=http://www.slate.com/id/2252063 | access-date=June 1, 2010 | journal=Slate | date=April 27, 2010 }}</ref>

====Thresholds in ecosystems (SAP 4.2)====

USGS released ''Thresholds of Climate Change in Ecosystems''<ref>[http://www.climatescience.gov/Library/sap/sap4-2/default.php CCSP, 2009] {{webarchive|url=https://web.archive.org/web/20090706024654/http://www.climatescience.gov/Library/sap/sap4-2/default.php |date=2009-07-06 }} Thresholds of Climate Change in Ecosystems (Fagre D.B., and C.W. Charles, lead authors) U.S. Geological Survey, Department of the Interior, Washington D.C., USADC. 156 pp.</ref> (SAP 4.2) on January 16, 2009.

A key premise of the report was that an [[ecological threshold]] is the point at which there is an abrupt change in an ecosystem that produces large, persistent and potentially irreversible changes. The report concluded that slight changes in climate may trigger major abrupt ecosystem responses that are not easily reversible. Some of these responses, including insect outbreaks, wildfire, and forest dieback, may adversely affect people as well as ecosystems and their plants and animals. One of the greatest concerns is that once an ecological threshold is crossed, the ecosystem in question will most likely not return to its previous state. The report also emphasized that human actions may increase an ecosystem's potential for crossing ecological thresholds. For example, additional human use of water in a watershed experiencing drought could trigger basic changes in aquatic life that may not be reversible. Ecosystems that already face stressors other than climate change, will almost certainly reach their threshold for abrupt change sooner.

====Effects on agriculture, land resources, water resources, and biodiversity (SAP 4.3)====

The [[United States Department of Agriculture]] released ''The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity''<ref>[http://www.climatescience.gov/Library/sap/sap4-3/default.php CCSP 2008.] {{webarchive|url=https://web.archive.org/web/20090507192513/http://www.climatescience.gov/Library/sap/sap4-3/default.php |date=2009-05-07 }} The Effects of Climate Change on Agriculture, Land Resources, Water Resources, and Biodiversity (Peter Backlund, Anthony Janetos, and David Schimel, convening lead authors) U.S. Department of Agriculture, Washington, DC., USA, 362 pp</ref> (SAP 4.3) in May 2008. The executive summary includes the following findings.

'''Agriculture'''

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====Adaptation options for climate-sensitive ecosystems and resources (SAP 4.4)====

EPA released ''Preliminary Review of Adaptation Options for Climate-Sensitive Ecosystems and Resources''<ref>[http://www.climatescience.gov/Library/sap/sap4-4/default.php CCSP, 2008] {{webarchive|url=https://web.archive.org/web/20090706025437/http://www.climatescience.gov/Library/sap/sap4-4/default.php |date=2009-07-06 }} Preliminary review of adaptation options for climate-sensitive ecosystems and resources. Susan H. Julius and Jordan M. West (editors). U.S. Environmental Protection Agency, Washington, DC, USA,. 873 pp</ref> (SAP 4.3) in May 2008. The study focuses on national parks, national forests, national wildlife refuges, wild and scenic rivers, national estuaries, and marine protected areas, all of which are protected by the federal

government. The report analyzed how to meet existing management goals set for each protected

area to understand what strategies will increase the resilience of each ecosystem.

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====''Effects of Climate Change on Energy Production and Use'' (SAP 4.5)====

DOE ''released Effects of Climate Change on Energy Production and Use in the United States''<ref>[http://www.climatescience.gov/Library/sap/sap4-5/default.php CCSP, 2007] {{webarchive|url=https://web.archive.org/web/20090706025452/http://www.climatescience.gov/Library/sap/sap4-5/default.php |date=2009-07-06 }}. Effects of Climate Change on Energy Production and Use in the United States. Thomas J. Wilbanks et al. (editors). Department of Energy, Office of Biological & Environmental Research, Washington, DC., USA, 160 pp.</ref> (SAP 4.5) in October 2007. The report concludes that the possible impacts of climate change on energy production are important enough to start considering how to adapt. The report's executive summary summarized the report with three questions and answers:

* ''How might climate change affect energy consumption in the United States?'' The research evidence is relatively clear that climate warming will mean reductions in total U.S. heating requirements and increases in total cooling requirements for buildings. These changes will vary by region and by season, but they will affect household and business energy costs and their demands on energy supply institutions. In general, the changes imply increased demands for electricity, which supplies virtually all cooling energy services but only some heating services. Other effects on energy consumption are less clear.

* ''How might climate change affect energy production and supply in the United States?'' The research evidence about effects is not as strong as for energy consumption, but climate change could affect energy production and supply (a) if extreme weather events become more intense, (b) where regions dependent on water supplies for hydropower and/or thermal power plant cooling face reductions in water supplies, (c) where temperature increases decrease overall thermoelectric power generation efficiencies, and (d) where changed conditions affect facility siting decisions. Most effects are likely to be modest except for possible regional effects of extreme weather events and water shortages.

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====''Effects on Human Health and Welfare and Human Systems'' (SAP 4.6)====

EPA released ''Analyses of the Effects of Global Change on Human Health and Welfare and Human Systems''.<ref>[http://www.climatescience.gov/Library/sap/sap4-6/default.php CCSP 2008] {{webarchive|url=https://web.archive.org/web/20090626134006/http://www.climatescience.gov/Library/sap/sap4-6/default.php |date=2009-06-26 }} Analyses of the effects of global change on human health and welfare and human systems. J.L. Gamble (editor). U.S. Environmental Protection Agency, Washington, DC, USA. 214pp214 pp</ref> (SAP 4.6) in July 2008. The report was directed by Janet L. Gamble of EPA and written by 28 authors.

According to EPA,<ref>[http://www.climatescience.gov/Library/sap/sap4-6/final-report/sap4-6-EPA-brochure.pdf Environmental Protection Agency 2008] {{webarchive|url=https://web.archive.org/web/20100527130550/http://www.climatescience.gov/Library/sap/sap4-6/final-report/sap4-6-EPA-brochure.pdf |date=2010-05-27 }} Findings of the U.S. Climate Change Science Program Synthesis and Assessment Product 4.6] Washington, D.CDC. 2 pp.</ref> some of the key conclusions of this report are:

* It is very likely that heat-related illnesses and deaths will increase over coming decades.

* An increase in ozone could cause or exacerbate heart and lung diseases.

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====Impacts on transport and infrastructure (SAP 4.7)====

The [[United States Department of Transportation]] released ''Impacts of Climate Variability and Change on Transportation Systems and Infrastructure—Gulf Coast Study''<ref>[http://www.climatescience.gov/Library/sap/sap4-7/default.php CCSP, 2008] {{webarchive|url=https://web.archive.org/web/20090706024709/http://www.climatescience.gov/Library/sap/sap4-7/default.php |date=2009-07-06 }} Impacts of Climate Change and Variability on Transportation Systems and Infrastructure: Gulf Coast Study, Phase I. M. J. Savonis, V.R. Burkett, and J.R. Potter (editors). Department of Transportation, Washington, DC, USA,. 445 pp.</ref> (SAP 4.7) in March 2008. The report was prepared by Michael Savonis of the Federal Highway Administration, Joanne Potter (a consultant to DOT), and Virginia Burkett of USGS.

The premise of SAP 4.7 was that climate is changing. Sea levels in the Gulf of Mexico are likely to rise by two to four feet over the next 50 to 100 years from the combination of climate-induced warming and land subsidence. Tropical storms are anticipated to increase in intensity and the number of heavy precipitation events is expected to increase, raising prospects of flooding and structural damage. And the number of very hot days (i.e., >90&nbsp;°F) could rise by 50%.

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===Using information to manage risks===

Three SAP's were prepared to further CCSP's Goal 5

* NASA released "Uses and Limitations of Observations, Data, Forecasts, and Other Projections in Decision Support for Selected Sectors and Regions."<ref>[http://www.climatescience.gov/Library/sap/sap5-1/default.php CCSP 2008] {{webarchive|url=https://web.archive.org/web/20090507192605/http://www.climatescience.gov/Library/sap/sap5-1/default.php |date=2009-05-07 }} Uses and Limitations of Observations, Data, Forecasts, and Other Projections in Decision Support for Selected Sectors and Regions. Washington, DDC.C. National Aeronautics and Space Administration. 90 pp.</ref> (SAP 5.1) in September 2008.

* NOAA released "Best Practice Approaches for Characterizing, Communicating, and Incorporating Scientific Uncertainty in Decisionmaking."<ref>[http://www.climatescience.gov/Library/sap/sap5-2/default.php CCSP, 2009] {{webarchive|url=https://web.archive.org/web/20090507192347/http://www.climatescience.gov/Library/sap/sap5-2/default.php |date=2009-05-07 }} Best practice approaches for characterizing, communicating, and incorporating scientific uncertainty in decisionmaking. Granger Morgan, H. Dowlatabadi, M. Henrion, [[David Keith (scientist)|D. Keith]], R. Lempert, S. McBrid, M. Small, T. Wilbanks (editors). National Oceanic and Atmospheric Administration, Washington D.C., USADC. 87 pp.</ref> (SAP 5.2) on January 16, 2009.

* NOAA released "Decision Support Experiments and Evaluations using Seasonal to Interannual Forecasts and Observational Data."<ref>[http://www.climatescience.gov/Library/sap/sap5-3/default.php CCSP, 2008] {{webarchive|url=https://web.archive.org/web/20090706024715/http://www.climatescience.gov/Library/sap/sap5-3/default.php |date=2009-07-06 }} Decision-Support Experiments and Evaluations using Seasonal-to-Interannual Forecasts and Observational Data: A Focus on Water Resources. Nancy Beller-Simms, Helen Ingram, David Feldman, Nathan Mantua, Katharine L. Jacobs, and Anne M. Waple (editors). National Climatic Data Center, Asheville, NC, 192 pp.</ref> (SAP 5.3) in November 2008.

===''Global Climate Change Impacts in the United States''===

To fulfill a statutory requirement for a [[National Assessment on Climate Change|national assessment]], the CCSP released ''Scientific Assessment of the Impacts of Global Change in the United States''<ref>[http://www.climatescience.gov/Library/scientific-assessment/ Scientific Assessment of the Impacts of Global Change in the United States, 2008] {{webarchive|url=https://web.archive.org/web/20090513010513/http://www.climatescience.gov/Library/scientific-assessment/ |date=2009-05-13 }}</ref> in May 2008. Shortly thereafter, a team of authors synthesized key findings from the SAP's. In June 2009, CCSP changed its name to United States Global Change Research Program and released the unified synthesis report, entitled ''Global Climate Change Impacts in the United States'' .<ref>[http://www.globalchange.gov/publications/reports/scientific-assessments/us-impacts/key-findings United States Global Change Research Program]. 2009. Global Climate Change Impacts in the United States. [[Washington, D.C.DC]] 188 pp</ref> The report had ten key findings which became the bedrock of the Obama Administration's view of the impacts of climate change.

# [[Climate Change Science Program#Temperature trends in the lower atmosphere (SAP 1.1)|''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.