Abstract
With an increasing political focus on limiting global warming to less than 2 � C above pre-industrial levels it is vital to understand the consequences of these targets on key parts of the climate system. Here, we focus on changes in sea level and sea ice, comparing twenty-first century pro- jections with increased greenhouse gas concentrations (using the mid-range IPCC A1B emissions scenario) with those under a mitigation scenario with large reductions in emis- sions (the E1 scenario). At the end of the twenty-first century, the global mean steric sea level rise is reduced by about a third in the mitigation scenario compared with the A1B scenario. Changes in surface air temperature are found to be poorly correlated with steric sea level changes. While the projected decreases in sea ice extent during the first half of the twenty-first century are independent of the season or scenario, especially in the Arctic, the seasonal cycle of sea ice extent is amplified. By the end of the century the Arctic becomes sea ice free in September in the A1B scenario in most models. In the mitigation scenario the ice does not disappear in the majority of models, but is reduced by 42 % of the present September extent. Results for Antarctic sea ice changes reveal large initial biases in the models and a sig- nificant correlation between projected changes and the initial extent. This latter result highlights the necessity for further refinements in Antarctic sea ice modelling for more reliable projections of future sea ice.
Highlights
Climate change and its adverse effects are of global concern
Building on the work by Hansen et al (2007), May (2008), and Washington et al (2009) this study investigates the possibility of reducing dangerous anthropogenic interference with the climate system by analyzing results from the ENSEMBLES multi-model experiments for the period 1860-2100
Our analysis focuses on two additional key aspects of climate change: steric sea level rise and sea ice change
Summary
Climate change and its adverse effects are of global concern. Article 2 of the United Nations Framework Convention on Climate Change (UNFCCC) states that the ultimate objective is the ‘‘stabilization of greenhouse gas (GHG) concentrations in the atmosphere at a level that would prevent dangerous anthropogenic interference with the climate system’’ (UNFCCC 1992). Within the ENSEMBLES project (Hewitt and Griggs 2004) a mitigation scenario named E1 was designed that would result in a global mean surface air temperature increase of less than 2 °C (Lowe et al 2009). Employing the GISS climate model, Hansen et al (2007) studied to what extent dangerous interference with the climate system may be realistically avoided In their regional analysis of the Arctic they find a clear distinction between the A1B scenario and the ‘‘alternative’’ scenario (Hansen and Sato 2004) that leads to a temperature rise of about 1 °C relative to today. The results are discussed and conclusions drawn (Sect. 5)
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