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Paul. J. Durack
154 Executive Summary
151 Executive summary
WG1 AR5 Ch4
152 References
151.5.1 Capabilities of Observations
151.4.2 Characterizing Uncertainty
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Ulrich Cubasch
Donald Wuebbles
Deliang Chen
Maria Cristina Facchini
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Paul. J. Durack
154 Executive Summary
151 Executive summary
WG1 AR5 Ch4
152 References
151.5.1 Capabilities of Observations
151.4.2 Characterizing Uncertainty
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Ulrich Cubasch
Donald Wuebbles
Deliang Chen
Maria Cristina Facchini
David Frame
Natalie Mahowald
Jan-Gunnar Winther
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151.2.3 Multiple Lines of Evidence for Climate Change
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While the first IPCC assessment depended primarily on observed changes in surface temperature and climate model analyses, more recent assessments include multiple lines of evidence for climate change. The first line of evidence in assessing climate change is based on careful analysis of observational records of the atmosphere, land, ocean and cryosphere systems (Figure 1.3). There is incontrovertible evidence from in situ observations and ice core records that the atmospheric concentrations of GHGs such as CO₂, CH<sub>4</sub>, and N₂O have increased substantially over the last 200 years (Sections 6.3 and 8.3). In addition, instrumental observations show that land and sea surface temperatures have increased over the last 100 years (Chapter 2). Satellites allow a much broader spatial distribution of measurements, especially over the last 30 years. For the upper ocean temperature the observations indicate that the temperature has increased since at least 1950 (Willis et al., 2010;<ref name="Willis 2010">Willis, J., D. Chambers, C. Kuo, and C. Shum, 2010: [http://www.tos.org/oceanography/archive/23-4_willis.html Global sea level rise recent progress and challenges for the decade to come]. Oceanography, 23, 26–35.</ref> Section 3.2). Observations from satellites and in situ measurements suggest reductions in glaciers, Arctic sea ice and ice sheets (Sections 4.2, 4.3 and 4.4). In addition, analyses based on measurements of the radiative budget and ocean heat content suggest a small imbalance (Section 2.3). These observations, all published in peer-reviewed journals, made by diverse measurement groups in multiple countries using different technologies, investigating various climate-relevant types of data, uncertainties and processes, offer a wide range of evidence on the broad extent of the changing climate throughout our planet. Conceptual and numerical models of the Earth’s climate system offer another line of evidence on climate change (discussions in Chapters 5 and 9 provide relevant analyses of this evidence from paleoclimatic to recent periods). These use our basic understanding of the climate system to provide self-consistent methodologies for calculating impacts of processes and changes. Numerical models include the current knowledge about the laws of physics, chemistry and biology, as well as hypotheses about how complicated processes such as cloud formation can occur. Because these models can represent only the existing state of knowledge and technology, they are not perfect; they are, however, important tools for analysing uncertainties or unknowns, for testing different hypotheses for causation relative to observations, and for making projections of possible future changes. One of the most powerful methods for assessing changes occurring in climate involves the use of statistical tools to test the analyses from models relative to observations. This methodology is generally called detection and attribution in the climate change community (Section 10.2). For example, climate models indicate that the temperature response to GHG increases is expected to be different than the effects from aerosols or from solar variability. Radiosonde measurements and satellite retrievals of atmospheric temperature show increases in tropospheric temperature and decreases in stratospheric temperatures, consistent with the increases in GHG effects found in climate model simulations (e.g., increases in CO₂, changes in O<sub>3</sub>), but if the Sun was the main driver of current climate change, stratospheric and tropospheric temperatures would respond with the same sign (Hegerl et al., 2007).<ref name="Hegerl">Hegerl, G. C., et al., 2007: [http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch9.html Understanding and attributing climate change]. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor and H. L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 665–745.</ref> Resources available prior to the instrumental period—historical sources, natural archives, and proxies for key climate variables (e.g., tree rings, marine sediment cores, ice cores)—can provide quantitative information on past regional to global climate and atmospheric composition variability and these data contribute another line of evidence. Reconstructions of key climate variables based on these data sets have provided important information on the responses of the Earth system to a variety of external forcings and its internal variability over a wide range of timescales (Hansen et al., 2006<ref name="Hansen 2006">Hansen, J., M. Sato, R. Ruedy, K. Lo, D. W. Lea, and M. Medina-Elizade, 2006: [http://www.pnas.org/content/103/39/14288.full Global temperature change]. Proc. Natl. Acad. Sci. U.S.A., 103, 14288–14293.</ref>; Mann et al., 2008)<ref name="Mann">Mann, M., Z. Zhang, M. Hughes, R. Bradley, S. Miller, S. Rutherford, and F. Ni, 2008:[http://www.pnas.org/content/early/2008/09/02/0805721105 Proxy-based reconstructions of hemispheric and global surface temperature variations over the past two millennia]. Proc. Natl. Acad. Sci. U.S.A., 105, 13252– 13257.</ref>. Paleoclimatic reconstructions thus offer a means for placing the current changes in climate in the perspective of natural climate variability (Section 5.1). AR5 includes new information on external RFs caused by variations in volcanic and solar activity (e.g., Steinhilber et al., 2009;<ref name="Steinhilber">Steinhilber, F., J. Beer, and C. Fröhlich, 2009: [http://onlinelibrary.wiley.com/doi/10.1029/2009GL040142/abstract Total solar irradiance during the Holocene]. Geophys. Res. Lett., 36, L19704.</ref> see Section 8.4). Extended data sets on past changes in atmospheric concentrations and distributions of atmospheric GHG concentrations (e.g., Lüthi et al., 2008;<ref name="Lüthi 2008">Lüthi, D., et al., 2008: [http://www.nature.com/nature/journal/v453/n7193/abs/nature06949.html High-resolution carbon dioxide concentration record 650,000– 800,000 years before present]. Nature, 453, 379–382.</ref> Beerling and Royer, 2011)<ref name="Beerling">Beerling, D. J., and D. L. Royer, 2011: [http://www.nature.com/ngeo/journal/v4/n7/index.html Convergent Cenozoic CO2 history]. Nature Geosci., 4, 418–420.</ref> and mineral aerosols (Lambert et al., 2008)<ref name="Lambert">Lambert, F., et al., 2008: [http://www.nature.com/nature/journal/v452/n7187/abs/nature06763.html Dust-climate couplings over the past 800,000 years from the EPICA Dome C ice core]. Nature, 452, 616–619.</ref> have also been used to attribute reconstructed paleoclimate temperatures to past variations in external forcings (Section 5.2). ==Notes== <references/> <center><font color=brown>Navigation</font><br /><font size=1 px>[[151 Executive summary|ES]] [[151.1 Chapter preview|1.1]] [[151.2.1 Setting the Stage for the Assessment|1.2.1]] [[151.2.2 Key Concepts in Climate Science|1.2.2]] [[151.2.3 Multiple Lines of Evidence for Climate Change|1.2.3]] [[151.3 Indicators of Climate Change|1.3]] [[151.3.1 Global and Regional Surface Temperatures|1.3.1]] [[151.3.2 Greenhouse Gas Concentrations|1.3.2]] [[151.3.3 Extreme Events|1.3.3]] [[151.3.4 Climate Change Indicators|1.3.4]] [[151.3.4.1 Sea Level|1.3.4.1]] [[151.3.4.2 Ocean Acidification|1.3.4.2]] [[151.3.4.3 Ice|1.3.4.3]] [[151.4.1 Uncertainty in Environmental Science|1.4.1]] [[151.4.2 Characterizing Uncertainty|1.4.2]] [[151.4.3 Treatment of Uncertainty in IPCC|1.4.3]] [[151.4.4 Uncertainty Treatment in This Assessment|1.4.4]] [[151.5 Advances in Measurement and Modelling Capabilities|1.5]] [[151.5.1 Capabilities of Observations|1.5.1]] [[151.5.2 Capabilities in Global Climate Modelling|1.5.2]] [[151.6 Overview and Road Map to the Rest of the Report|1.6]] [[Box 151.1 Description of Future Scenarios|Box 1]] [[151 Frequently asked questions|FAQ]] [[151 References|Refs]]</font></center>
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