Publications

Duffy, P.B., B.D. Santer and T.M.L. Wigley. 2009: Solar variability does not explain late-20th-century warming. Physics Today, 62, 48-49. [article]

Figure 1: High resolution figure

The hypothesis of Nicola Scafetta and Bruce West (see their Opinion piece, PHYSICS TODAY, March 2008, page 50), that most of the observed global warming trend since 1950 is due to variations in total solar irradiance (TSI), is at odds with observations and theory. They argue that near-surface temperatures are strongly influenced by both the well-known 11-year cycle in TSI and shorter-time-scale TSI variations.

Figure caption: Observed monthly global temperature anomalies since 1950. The red curve is the HadCRUT3v data set of global-mean near-surface air temperature, T_s, the standard meteorological temperature measurement. The blue curve is a 10-year running mean. (Data are from the climatic research unit, University of East Anglia, UK.)

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Santer, B.D., P.W. Thorne, L. Haimbergr, K.E. Taylor, T.M.L. Wigley, J.R. Lanzante, S. Solomon, M. Free, P.J. Gleckler, P.D. Jones, T.R. Karl, S.A. Klein, C. Mears, D. Nychka, G.A. Schmidt, S.C. Sherwood and F.J. Wentz. 2008: Consistency of modelled and observed temperature trends in the tropical troposphere. International Journal of Climate, 28, 1703-1722, doi:10.1002/joc.1756.

Figure 2: High resolution figure

Abstract: A recent report of the U.S. Climate Change Science Program (CCSP) identified a potentially serious inconsistency between modelled and observed trends in tropical lapse rates (Karl et al., 2006). Early versions of satellite and radiosonde datasets suggested that the tropical surface had warmed more than the troposphere, while climate models consistently showed tropospheric amplification of surface warming in response to human-caused increases in well-mixed greenhouse gases (GHGs). We revisit such comparisons here using new observational estimates of surface and tropospheric temperature changes. We find that there is no longer a serious discrepancy between modelled and observed trends in tropical lapse rates. This emerging reconciliation of models and observations has two primary explanations. First, because of changes in the treatment of buoy and satellite information, new surface temperature datasets yield slightly reduced tropical warming relative to earlier versions. Second, recently developed satellite and radiosonde datasets show larger warming of the tropical lower troposphere. In the case of a new satellite dataset from Remote Sensing Systems (RSS), enhanced warming is due to an improved procedure of adjusting for inter-satellite biases. When the RSS-derived tropospheric temperature trend is compared with four different observed estimates of surface temperature change, the surface warming is invariably amplified in the tropical troposphere, consistent with model results. Even if we use data from a second satellite dataset with smaller tropospheric warming than in RSS, observed tropical lapse rate trends are not significantly different from those in all other model simulations. Our results contradict a recent claim that all simulated temperature trends in the tropical troposphere and in tropical lapse rates are inconsistent with observations. This claim was based on use of older radiosonde and satellite datasets, and on two methodological errors: the neglect of observational trend uncertainties introduced by interannual climate variability, and application of an inappropriate statistical consistency test.

Figure caption: Comparisons of simulated and observed trends in tropical T_2LT over January 1979 to December 1999.

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Van Vuuren, D.P., M. Meinshausen, G.-K. Plattner, F. Joos, K.M. Strassmann, S.J. SMith, T.M.L. Wigley, S.C.B. Raper, K. Riahi, F. de la Chesnaye, M.G.J. den Elzen, J. Fujino, K. Jiang, N. Nakicenovic, S. Paltsev and J.M. Reilly. 2009: Temperature increase of 21st century mitigation scenarios. Proc. of the Nat. Acad. of Sci. of USA, 105, 15258-15262, doi:10.1073/pnas.0711129105 .

Figure 3: High resolution figure

Abstract: Estimates of 21st Century global-mean surface temperature increase have generally been based on scenarios that do not include climate policies. Newly developed multigas mitigation scenarios, based on a wide range of modeling approaches and socioeconomic assumptions, now allow the assessment of possible impacts of climate policies on projected warming ranges. This article assesses the atmospheric CO2 concentrations, radiative forcing, and temperature increase for these new scenarios using two reduced-complexity climate models. These scenarios result in temperature increase of 0.5–4.4°C over 1990 levels or 0.3–3.4°C less than the no-policy cases. The range results from differences in the assumed stringency of climate policy and uncertainty in our understanding of the climate system. Notably, an average minimum warming of ˜1.4°C (with a full range of 0.5–2.8°C) remains for even the most stringent stabilization scenarios analyzed here. This value is substantially above previously estimated committed warming based on climate system inertia alone. The results show that, although ambitious mitigation efforts can significantly reduce global warming, adaptation measures will be needed in addition to mitigation to reduce the impact of the residual warming.

Figure caption: Radiative forcing and temperature change in year 2100 (A and B), transient temperature change (C) and 2100 temperature increase as a function of cumulative emissions (D). Radiative forcing relative to a preindustrial state and temperature change relative to 1980–2000 are given for baseline (red) and mitigation (blue) scenarios (A and B). Central values are shown as symbols and uncertainty ranges as color bands.