The downward radiation to the surface increases mainly because the low
level air temperature increases, not because of the direct effect of increased CO2 in the air.
A comparison of the moraine ages with nearby climate records indicates that Rwenzori glaciers expanded contemporaneously with regionally dry, cold conditions and retreated
when air temperature increased.
While 2009 showed a slowdown in the rate of
annual air temperature increases in the Arctic, the first half of 2010 shows a near record pace with monthly anomalies of over 4 °C in northern Canada.
Modelled surface
air temperature increases in all regions and seasons, with most land areas warming more rapidly than the global average (Giorgi et al., 2001; Ruosteenoja et al., 2003).
Air temperature increases similar to those observed aloft since 1960, amplified by associated increases in humidity, account for a significant portion of the enhanced ablation leading to this strongly negative mass balance, but the exact proportion is highly uncertain because of the short span of energy and mass balance observations.
During that season, the Arctic air mixes less than in the summer, because of cold temperatures and inversion layers — places
where air temperature increases with height, instead of the other way around.
«The pattern of decreasing tree cover and increasing impervious surfaces indicate a synergistic pattern of loss of environmental benefits (e.g., air temperature cooling by trees) and increased environmental issues (e.g.,
air temperature increases associated with impervious surfaces),» the authors write in their study.
The researchers also found that planting trees between 30 - 50 degrees latitude worldwide saw the global mean
surface air temperature increase by 0.7 degrees Fahrenheit.
Detailed studies of the energy balance and ablation of the Zongo and Chacaltaya glaciers support the importance
of air temperature increase, and identify the increase in downward infrared radiation as the main way that the effect of the warmer air is communicated to the glacier surface [Wagnon et al. 1999; Francou et al, 2003].
These facts help explain why, in spite of the Earth's
air temperature increasing to a level that the IPCC claims is unprecedented in the the past millennium or more, a recent study by Randall et al. (2013) found that the 14 % extra carbon dioxide fertilization caused by human emissions between 1982 and 2010 caused an average worldwide increase in vegetation foliage by 11 % after adjusting the data for precipitation effects.
Had the sensitivity been 3.4 °C for a 2xCO2, and had Hansen decreased the radiative forcing in Scenario B slightly, he would have correctly projected the ensuing global surface
air temperature increase.