David Ward Royal Society

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</div><div><h2 style="font-family: "Times New Roman"; margin: 1em 0px 0.25em; padding: 0px; overflow: hidden; border-bottom: 1px solid rgb(162, 169, 177); font-weight: normal; line-height: 1.3;">Conclusions[</h2><h3 style="font-family: "Times New Roman"; background-color: rgb(255, 255, 255); margin: 0.3em 0px 0px; padding-top: 0.5em; padding-bottom: 0px; overflow: hidden; line-height: 1.6;">Working Group I[</h3>The key conclusions of Working Group I (<a rel="nofollow" class="external text" href="http://www.grida.no/climate/ipcc_tar/wg1/005.htm" w="w" skins="skins" vector="Vector" resources="resources" skins.vector.styles="skins.vector.styles" images="images" external-link-ltr-icon.svg="external-link-ltr-icon.svg" b4b84="b4b84" right="right" center="center" no-repeat="no-repeat" padding-right="padding-right" px="px" style="text-decoration-line: none; background: url("");">The Scientific Basis, Summary for Policymakers</a>, in <a href="https://en.wikipedia.org/wiki/IPCC_Third_Assessment_Report#CITEREFIPCC_AR3_WG12001" style="text-decoration-line: none; background: none;">IPCC AR3 WG1 2001</a>) were:<ol style="font-family: "Times New Roman"; font-size: large; margin: 0.3em 0px 0px 3.2em; padding: 0px; list-style-image: none;"><li style="margin-bottom: 0.1em;">An increasing body of observations gives a collective picture of a warming world and other changes in the climate system (The global <a href="https://en.wikipedia.org/wiki/Instrumental_temperature_record" title="Instrumental temperature record" style="background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">average surface temperature</a> has increased over the 20th century by about 0.6 °C; Temperatures have risen during the past four decades in the lowest 8 kilometres of the atmosphere; Snow cover and ice extent have decreased)</li><li style="background-color: rgb(255, 255, 255); margin-bottom: 0.1em;">Emissions of greenhouse gases and aerosols due to human activities continue to alter the atmosphere in ways that are expected to affect the climate (Anthropogenic <a href="https://en.wikipedia.org/wiki/Aerosol" title="Aerosol" style="text-decoration-line: none; background: none;">aerosols</a> (i.e., human emitted aerosols) are short-lived and mostly produce negative radiative forcing; Natural factors have made small contributions to <a href="https://en.wikipedia.org/wiki/Radiative_forcing" title="Radiative forcing" style="text-decoration-line: none; background: none;">radiative forcing</a> over the past century)</li><li style="margin-bottom: 0.1em;">Confidence in the ability of models to project future climate has increased (Complex physically based climate models are required to provide detailed estimates of feedbacks and of regional features. Such models cannot yet simulate all aspects of climate (e.g., they still cannot account fully for the observed trend in the surface-troposphere temperature difference since 1979) and there are particular uncertainties associated with clouds and their interaction with radiation and aerosols. Nevertheless, confidence in the ability of these models to provide useful projections of future climate has improved due to their demonstrated performance on a range of space and time-scales <a rel="nofollow" class="external autonumber" href="http://www.grida.no/climate/ipcc_tar/wg1/007.htm" w="w" skins="skins" vector="Vector" resources="resources" skins.vector.styles="skins.vector.styles" images="images" external-link-ltr-icon.svg="external-link-ltr-icon.svg" b4b84="b4b84" right="right" center="center" no-repeat="no-repeat" padding-right="padding-right" px="px" style="background-image: url(""); background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">[3]</a>.)</li><li style="margin-bottom: 0.1em;">There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities</li><li style="background-color: rgb(255, 255, 255); margin-bottom: 0.1em;">Human influences will continue to change atmospheric composition throughout the 21st century</li><li style="margin-bottom: 0.1em;">Global average temperature and sea level are projected to rise under all IPCC <a href="https://en.wikipedia.org/wiki/Special_Report_on_Emissions_Scenarios" title="Special Report on Emissions Scenarios" style="background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">SRES scenarios</a>.</li></ol>The TAR estimate for the <a href="https://en.wikipedia.org/wiki/Climate_sensitivity" title="Climate sensitivity" style="background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">climate sensitivity</a> is 1.5 to 4.5 °C; and the average surface temperature is projected to increase by 1.4 to 5.8 Celsius degrees over the period 1990 to 2100, and the sea level is projected to rise by 0.1 to 0.9 metres over the same period. The wide range in projections is based upon several different scenarios that assume different levels of future CO2 emissions (see the section below on <a href="https://en.wikipedia.org/wiki/IPCC_Third_Assessment_Report#Projections_in_the_TAR" title="IPCC Third Assessment Report" style="background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">Projections in the TAR</a>).<h3 style="font-family: "Times New Roman"; background-color: rgb(255, 255, 255); margin: 0.3em 0px 0px; padding-top: 0.5em; padding-bottom: 0px; overflow: hidden; line-height: 1.6;">Synthesis Report[</h3>The TAR Synthesis Report includes a summary of the TAR's main findings and uncertainties.<a href="https://en.wikipedia.org/wiki/IPCC_Third_Assessment_Report#cite_note-tar_robust_findings_and_key_uncertainties-2" style="text-decoration-line: none; background: none;">[2]</a> "Robust findings" of the TAR include:<a href="https://en.wikipedia.org/wiki/IPCC_Third_Assessment_Report#cite_note-tar_robust_findings_and_key_uncertainties-2" style="text-decoration-line: none; background: none;">[2]</a><ul w="w" skins="skins" vector="Vector" resources="resources" skins.vector.styles="skins.vector.styles" images="images" bullet-icon.svg="bullet-icon.svg" d4515="d4515" margin="margin" em="em" px="px" padding="padding" style="font-family: "Times New Roman"; font-size: large; list-style-image: url("");"><li style="margin-bottom: 0.1em;">Observed warming of the Earth's surface, attribution of observed warming to human activities, <a href="https://en.wikipedia.org/wiki/Global_climate_model#Projections_of_future_climate_change" class="mw-redirect" title="Global climate model" style="background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">projected increases</a> in future global mean temperature, rising <a href="https://en.wikipedia.org/wiki/Current_sea_level_rise" class="mw-redirect" title="Current sea level rise" style="background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">sea levels</a>, and increased frequency of <a href="https://en.wikipedia.org/wiki/Heat_wave" title="Heat wave" style="background-image: none; background-position: initial; background-size: initial; background-repeat: initial; background-attachment: initial; background-origin: initial; background-clip: initial; text-decoration-line: none;">heat waves</a>.</li><li style="margin-bottom: 0.1em;">Future warming will have both beneficial and adverse effects, but for higher levels of warming, adverse effects will predominate.</li><li style="margin-bottom: 0.1em;">Developing countries and poor persons are most vulnerable to climate change.</li></ul></div>