Following on from an earlier study in 2005 that indicated glaciers in the Karakoram Himalaya have not followed the general trend of glacier retreat observed in other parts of the Himalayas, Hewitt (2011) undertook a review of the literature to investigate the later Little Ice Age in the Karakoram and the recent 'expansion' of the glaciers in the region. From a review of the literature, Hewitt (2011) observed that on average, Karakoram glaciers only declined by 5% between 1920 and 1960, becoming almost static in the 1970s, with some glaciers advancing during this period. From the studies, generally rates of retreat were resumed in the 1980s and into the early 1990s but were largely insignificant and since the 1990s a stabilisation of the glacial balance and advances in the High Karakoram (coinciding with increases in snow cover) were observed.
Hewitt (2011) attributes the relatively static response to global warming of the Karakoram glaciers to their relatively high-elevation 'buffering' against rising atmospheric carbon dioxide levels. Due to the higher altitude, precipitation in the region mainly falls as snow throughout the year, and Hewitt (2011) states that the warmer ocean temperatures may also contribute to greater moisture systems reaching the region. In addition to this, local studies have observed a recent cooling in summer temperatures coinciding with increased cloudiness and greater snow cover, an observation that Hewitt (2011) suggests could be due to the albedo feedback.
Thus, this article suggests that whilst glaciers are retreating across the Himalayas, this cannot be generalised to all glaciers in the region and highlights the complex interaction of feedback mechanisms that control an individual glacier's response to global warming.
OUTLOOK ON CLIMATE CHANGE: MUCH OF THE SAME OR EVEN WORSE!
In preparation for the fifth IPCC report due for 2013 a meeting was held this week by climate scientists to assess any advancements in our knowledge of our changing climate since the last report almost five years ago. Overall, although there has been substantial improvements in modelling, with larger, more sophisticated and integrated models than five years ago, the simulations being produced have remained relatively similar (Science, 2011). Results from one-third of the thirty models expected to be used in AR5, were only slightly more sensitive to greenhouse gas emissions than the past AR4 model and predict similar regional patterns of temperature and precipitation changes throughout the world.
However, some of the simulated responses to global warming in the most recent models did diverge from past estimations. For example the AR4 (2007) report estimated ice sheet melt would contribute to around a 25cm rise in sea levels by 2100. The increased sensitivity of the latest models has increased this value to 32cm, which is higher than the IPCC last conservative estimate but substantially lower than earlier estimates of one metre (Science, 2011). Incorporation of this new value produces a range of cumulative sea level rise from ocean thermal expansion, ice and glacial melt between 63 to 71cm by 2100, a sufficient level to inundate a substantial area of Bangladesh.
Although the meeting did not review all of the models or studies that will be included in the final report, conclusions from the meeting confirm our current understanding of the rate of global warming and the regional impacts that it could have around the world. Despite minimal changes in the observations of the models, this still supports the claim that global warming is occurring and should be seen as evidence for action to be taken to attempt to minimise or reverse this rising trend. Due to the complexity of the Earth's systems, uncertainty can never be removed from models of climate change. However, the consistency between the models analysed in this meeting and models from the last report suggest that the observed warming trend is not anomalous and the simulated regional responses to global warming are likely, within their observed ranges, to occur.
Reference
Hewitt, K. 2011. Glacier change, concentration, and elevation effects in the Karakoram Himalaya, upper Indus Basin. Mountain Research and Development , 31: 188-200.
Science, 2011 'Climate outlook looking much the same, or worse', Science, 334, 1616
No comments:
Post a Comment