Another reminder from Dave Roberts, — http://grist.org/author/david-roberts/
We know we’ve raised global average temperatures around 0.8 degrees C so far. We know that 2 degrees C is where most scientists predict catastrophic and irreversible impacts. And we know that we are currently on a trajectory that will push temperatures up 4 degrees or more by the end of the century.
What would 4 degrees look like? World Bank review of the science reminds us. First, it’ll get hot:
Projections for a 4°C world show a dramatic increase in the intensity and frequency of high-temperature extremes. Recent extreme heat waves such as in Russia in 2010 are likely to become the new normal summer in a 4°C world. Tropical South America, central Africa, and all tropical islands in the Pacific are likely to regularly experience heat waves of unprecedented magnitude and duration. In this new high-temperature climate regime, the coolest months are likely to be substantially warmer than the warmest months at the end of the 20th century. In regions such as the Mediterranean, North Africa, the Middle East, and the Tibetan plateau, almost all summer months are likely to be warmer than the most extreme heat waves presently experienced. For example, the warmest July in the Mediterranean region could be 9°C warmer than today’s warmest July.
Extreme heat waves in recent years have had severe impacts, causing heat-related deaths, forest fires, and harvest losses. The impacts of the extreme heat waves projected for a 4°C world have not been evaluated, but they could be expected to vastly exceed the consequences experienced to date and potentially exceed the adaptive capacities of many societies and natural systems. [my emphasis]
Warming to 4 degrees would also lead to “an increase of about 150 percent in acidity of the ocean,” leading to levels of acidity “unparalleled in Earth’s history.” That’s bad news for, say, coral reefs:
The combination of thermally induced bleaching events, ocean acidification, and sea-level rise threatens large fractions of coral reefs even at 1.5°C global warming. The regional extinction of entire coral reef ecosystems, which could occur well before 4°C is reached, would have profound consequences for their dependent species and for the people who depend on them for food, income, tourism, and shoreline protection.
It will also “likely lead to a sea-level rise of 0.5 to 1 meter, and possibly more, by 2100, with several meters more to be realized in the coming centuries.” That rise won’t be spread evenly, even within regions and countries — regions close to the equator will see even higher seas.