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Spurious correlations between these forcings during the 20th century (North and 14 Stevens, 1998) and the uncertain time-evolution of solar forcing (see Section 9.2.1.3) have so far hindered a 15 reliable estimate of the observed response to solar forcing. However, even with large amplifications of the 16 HadCM3’s response to solar forcing, the conclusion of the TAR still holds that most of the warming over the 17 last 50 years of the 20th century is attributable to increasing greenhouse gas concentrations.

., 2004) including northern Alaska, where the date 11 of snowmelt has advanced about 8 days since the mid-1960s (Stone et al., 2002). In New England 12 (northeastern U.S.), a reduction in spring snow is implied by the 1-2 week advance in spring snowmelt 13 runoff that has occurred mostly since 1970 (Hodgkins et al. (2003). 14 15 Another dimension of change in snow is provided by the annual measurements of mountain SWE near April 16 1 in western North America, which indicate declines since 1950 at about 75% of locations monitored (Mote 17 et al., 2005).

Adjustments for this problem also remove an artificial cooling that occurs due to a 30 switch from afternoon to morning observation times for the U.S. Cooperative Observer Network (Vose et al., 31 2004). 32 33 Adjustments for urban impacts on temperature data have been limited to approaches such as linear regression 34 against population (Karl et al., 1988).

Asia 116.2 -1322 -265 0.09 -1128 -256 0.08 -464 -363 0.12 Alaska + Coast Mtns. 90.0 -2312 -600 0.15 -1892 -550 0.14 -1102 -1110 0.28 NW-USA + SW-CAN 39.2 -848 -503 0.05 -771 -518 0.06 -193 -447 0.05 Europe 17.3 -32 -43 0.00 23 35 -0.00 -72 -378 0.02 Patagonian Ice Fields 19.9 -726 -850 0.05 -588 -780 0.04 -351 -1680 0.09 S.America - PIF 4.7 -21 -103 0.00 -12 -68 0.00 -17 -333 0.00 a Antarctica 176.0 -737 -97 0.05 -469 -70 0.03 -408 -211 0.10 b Total 778.3 -7953 -240 0.510 -6191 -210 0.43 -3495 -400 0.88 b Total SLEB (mm) 22 17.1 9.6 27 Notes: 32 28 (a) Includes the Subantarctic islands (7 × 10 km) 29 (b) Not included are glaciers in New Zealand, Kamchatka, Siberia and the tropics for which no respective data or 30 reliable extrapolation are available.

Glick, 1999: Interannual variation of the Madden-Julian Oscillation 20 during austral summer. J. Climate, 12, 2538-2550. 21 Hewitt, C.D., C.S. Senior, and J.F.B. Mitchell, 2001: The impact of dynamic sea-ice on the climate 22 sensitvity of a GCM: a study of past, present and future climates, Clim Dyn., 17, 655-668. 23 Heymsfield, A.J., and L.Donner, 1990: A scheme for parameterizingice-cloud water content in general 24 circulationmodels.

Adjustments for this problem also 20 remove an artificial cooling that occurs due to a switch from afternoon to morning observation times for the 21 U.S. Cooperative Observer Network (Vose et al., 2004). 22 23 Estimates of urban impacts on temperature data have included approaches such as linear regression against 24 population (Karl et al., 1988), and analysis of differences between urban and rural sites defined by vegetation 25 (Gallo et al., 2002) or night lights (Peterson, 2003) as seen from satellites.

Since a considerable portion of the world population live in urban 48 environments (and this proportion may very well increase), many people will be exposed to even warmer 49 local climates due to increased urban heat island effects, especially through increases in mean daily 50 minimum temperatures, a variable known to have health consequences (Meehl and Tebaldi, 2004). 51 52 Most areas well suited to large scale agriculture have already been converted to this land use/cover type. 53 These areas include western Europe, the eastern U.S., eastern China, South America and portions of South 54 Africa and southeastern Australia. Land-cover conversion to agriculture is likely to continue in the future, 55 especially in parts of the western North America, tropical areas of south and central America, and arable 56 regions in Africa and south and central Asia (IPCC, 2001; RIVM, 2002).

In the last 50 years, several regions of the world have seen cropland 9 areas stabilize, and even decrease (Figure 2.5.1) In the U.S., as cultivation shifted from the east to the 10 Midwest, croplands were abandoned along the eastern seaboard around the turn of the century, the eastern 11 forests have undergone a regeneration over the last century.

Dai, 2004a: Response of the Atlantic thermohaline 6 circulation to increased atmospheric CO2 in a coupled model. J. Clim., 17, 4267-4279. 7 Hu, Z.Z., E.K. Schneider, U.S. Bhatt, and B.P. Kirtman, 2004b: Potential mechanism for response of El 8 Niño-Southern Oscillation variability to change in land surface energy budget.

The RF bar chart is now broken into aerosol components (sulfate, fossil-fuel soot, and 16 biomass burning aerosols) with a separate range for indirect effects. 17 18 During the 1990s there were concerted research programs in the U.S. and EU to evaluate the global 19 environmental impacts of aircraft, both the current civil aviation and a proposed supersonic fleet.