The new projections, based on advanced computer models and a thorough review of recent extreme heatwaves, are more concerning than the findings of the UN climate scientists from last year. The Intergovernmental Panel on Climate Change report stated that heatwaves are very likely to become more frequent and intense this century. Monthly heat extremes in summer are already affecting five percent of the world's land area, with this number expected to double by 2020 and quadruple by 2040, according to a study published in Environmental Research Letters. The tropics will be most impacted by increased heatwaves, followed by regions such as the Mediterranean, Middle East, parts of western Europe, central Asia, and the United States. Without reducing greenhouse gas emissions, it is projected that by the end of the century, the coldest summer months in many areas will be hotter than the hottest temperatures experienced today. The IPCC attributes the rising temperatures and extreme weather events to heat-trapping gases, primarily from burning fossil fuels. Nearly 200 governments have agreed to limit global warming to below 2 degrees Celsius above pre-industrial levels and are working towards a deal to reduce greenhouse gas emissions by the end of 2015. Global average surface temperatures have already increased by 0.8C since the Industrial Revolution.