Revised 21st century temperature projections

Abstract

Temperature projections for the 21st century made in the Third Assessment Report (TAR) of the United Nations Intergovernmental Panel on Climate Change (IPCC) indicate a rise of 1.4 to 5.8°C for 1990-2100. However, several independent lines of evidence suggest that the projections at the upper end of this range are not well supported. Since the publication of the TAR, several findings have appeared in the scientific literature that challenge many of the assumptions that generated the TAR temperature range. Incorporating new findings on the radiative forcing of black carbon (BC) aerosols, the magnitude of the climate sensitivity, and the strength of the climate/carbon cycle feedbacks into a simple upwelling diffusion/energy balance model similar to the one that was used in the TAR, we find that the range of projected warming for the 1990-2100 period is reduced to 1.1-2.8°C. When we adjust the TAR emissions scenarios to include an atmospheric CO 2 pathway that is based upon observed CO 2 increases during the past 25 yr, we find a warming range of 1.5-2.6°C prior to the adjustments for the new findings. Factoring in these findings along with the adjusted CO 2 pathway reduces the range to 1.0-1.6°C. And thirdly, a simple empirical adjustment to the average of a large family of models, based upon observed changes in temperature, yields a warming range of 1.3-3.0°C, with a central value of 1.9°C. The constancy of these somewhat independent results encourages us to conclude that 21st century warming will be modest and near the low end of the IPCC TAR projections.

Changes in temperature and precipitation in the instrumental period (1951–2018) and projections up to 2100 in Podgorica (Montenegro)

“…It is possible that models overestimate the rise (fall) of a given climate element and underestimate the impact of certain factors on climate. Other authors also noted that the temperature projections reported by the IPCC in its reports were overestimated, especially for the more extreme variants (Michaels et al, 2002;Ongoma et al, 2018). The uncertainties of climate models was discussed in the work of Laprise et al (2008), Holtanová et al (2014), Sanderson et al (2017).…”

Keeping it simple: the value of an irreducibly simple climate model

“…Reasons for this hot running were discussed. The simple model, using parameter values consistent with a growing body of papers [e.g., 7–33] that report climate sensitivity to be below current central estimates, showed that in at least five significant respects the general-circulation models’ approach was questionable:The assumption that temperature feedbacks will double or triple direct warming is unsound. Feedbacks may well reduce warming, not amplify it (see, e.g., [16, 19]).…”

Host plants and butterfly biology. Do host‐plant strategies drive butterfly status?

“…Two basic pressures are usually implicated in such events: climatic change (e.g. Malhi, 2002;Michaels et al, 2002;Reay, 2002;Greenland et al, 2003) and changes in agricultural land-use resulting in massive inputs of fertilisers, regular mechanised disturbance (biotope degradation), and the concomitant replacement of relatively unproductive, undisturbed habitats with highly productive and highly disturbed ones (Ratcliffe, 1984;Hodgson, 1986).…”