Senator Inhofe on Climate Change

All quantitative paleoclimate reconstructions of the past millennium published in the scientific literature have come to the opposite conclusion. They consistently find that late 20th century warmth is anomalous in the context of at least the last 1000 years for the Northern Hemisphere on the whole. Though certain regions appear to have exhibited mild conditions during the so-called “Medieval Warm Period”, there is no credible evidence we are aware of that average temperatures for the Northern Hemisphere or globe were as warm as (let alone warmer than) the late 20th century.

Inhofe then attempts to criticize the “Hockey Stick” reconstruction by citing a modeling study by the German GKSS group that actually supports the “Hockey Stick” conclusion that late 20th century warmth is anomalous in the context of the past 1000 years (see GKSS curve in Figure ) as well as the conclusion that this warmth can only be attributed to anthropogenic influences.

Furthermore, he attempts to criticize the methodology underlying the Mann et al (1998) reconstruction (one of more than a dozen estimates coming to essentially the same “Hockey Stick” conclusion), based on a reference to a comment by “three geophysicists from the University of Utah” [Chapman et al (2004)–see the response here] related to a modeling study by Mann and Schmidt (2003). That study has nothing to do with the Mann et al (1998) temperature reconstructions or methodology whatsoever (and did not even reference them) , but instead analyzed the factors governing the difference between ground surface temperature and land air temperature change in a climate model simulation of the latter 20th century.

(2) Global Sea level Rise

Estimates from tide gauges indicate that sea level has changed at the rate of 1.8 to 2.4 mm/yr over the last century. Satellite altimeter estimates currently show a global sea level change of 2.8+/- 0.4 mm/yr over the last 12 years. Due to the different methodologies involved, a direct comparison of the two values is not straightforward, but the satellite results provide absolutely no support for Inhofe’s contention that “there is a total absence of any recent acceleration in sea level rise”.

(3) Recent Arctic warming

Inhofe contends that “current Arctic temperature is no higher than temperatures in 1930s and 1940s” and cites many studies that appear to agree with him. However, the context for those studies is important and was well covered in the Arctic Climate Impact Assesment. In particular, natural variability in the climate system is particularly large in the high latitudes, such as the Arctic. This implies that temperatures from any one or two years may not be very representative of a long term trend. Arctic temperatures did indeed have a peak around 1940, but the decadal mean temperatures are now (1995-2004) warmer than the mean over 1935-1944. The variations in temperature in the Arctic resemble the global mean changes over the last century but are larger, clearly demonstrating the effect of polar amplification. More important are the causes of these temperature changes, and this cannot be determined simply by looking at one time series (this is further discussed here). The current consensus view is that warming in the 1940s was likely a combination of increasing GHG and solar forcing combined with a significant amount of internal variability, particularly associated with the North Atlantic. The subsequent cooling was related to the post-war increase in (mainly) sulphate aerosols. Subsequent to the 1970’s greenhouse gas forcing has become dominant, leading to the recent warming.

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