IPCC scientists report: a summary.

Guardian: “The global climate has already changed in many ways that are unprecedented in the past hundreds or thousands of years, the world’s scientists and governments concluded in the new report from the Intergovernmental Panel on Climate Change.” “These changes have affected every region of the globe, on land and at sea. Continued carbon emissions will drive further heatwaves, sea level rise, melting ice and extreme weather. The changes will last for centuries and limiting the effects would require “substantial and sustained” cuts in carbon dioxide, the scientists report.”
Scientists are now at least 66% certain that the last three decades are the warmest in 1400 years, with global temperature having risen by 0.9C in the last century. However, more than 90% of the heat trapped by greenhouse gases is being stored in the oceans.
….The scientists predict the average temperature between 2080 and 2100 will be 2.6-4.8C higher than today if emissions are unchecked.
…The new projections for the average sea level in the period 2080-2100 are greater than in the 2007 report, ranging from 45-82cm higher than now if nothing is done to curb emissions to 26-55cm if carbon emissions are halted and reversed. In the former case, sea level could have risen by a 98cm by the end of the century, seriously threatening cities from Shanghai to New York and meaning hurricanes and cyclones inflict far worse damage when they hit shorelines.
Sea level projections have been controversial because exactly how fast glaciers and ice sheets will slip into the sea is not well known. A collapse in ice sheets is therefore not included in the estimates and could add tens of centimetres more to the rise. Because the big Greenland and Antarctic ice sheets are slow to melt, scientists predict melting and sea level rise will continue for centuries. If a temperature rise of between 1C and 4C is sustained, the vast Greenland ice sheet will completely melt adding 7m to sea level, scientists predict, but over the course of a millennium.
….The impact of warming is crystal clear in the faster rates of melting in virtually all the world’s glaciers and the huge ice sheets in Greenland and Antarctica. The ice sheets have been shedding at least five times more water in the 2000s than in the 1990s, the scientists report.
Scientists are 90% sure that Arctic sea ice, snow cover and glaciers will continue to shrink. The scientists say a “nearly ice-free” Arctic ocean in September is at least 66% likely before 2050.
….The last decade has been the warmest on record but although CO2 concentrations in the atmosphere have continued to accelerate, surface air temperatures have only marginally increased in the past 15 years, leading some to suggest global warming has stopped. The IPCC scientists reject this, reporting that while the warming trend is robust over decades, there is “substantial” variability within decades. They conclude: “Trends based on short records … do not in general reflect long-term climate trends.”
They add that the heat being trapped by global warming in 2011 was 43% more than the estimate for 2005 in their last report and that over 90% of all the heat added enters the oceans.
….Scientists calculate that nearly half of all the carbon dioxide that can be safely emitted without raising temperatures above a dangerous 2C has already been emitted. This, says the IPCC, means governments must act quickly to have a reasonable change of avoiding 2C.”