The Intergovernmental Panel on Climate Change (IPCC) has released a new, very important report. It was created with the help of 1250 experts, and approved by 194 governments, which is probably even harder than it sounds. It confirms some things that we already knew about climate change and turns up the urgency dial on other things.
One of the main messages is that business as usual is not an option. It would lead to temperature increases of between 3.7 celsius (C) and 4.8C, which is far above the 2C threshold that scientists agree would lead to much more catastrophic warming. Even reaching the pledges made at the Cancun Climate Convention in 2010 wouldn't be enough to stay below that 2C level, and would bring us closer to 3C.
Not going over the 2C limit is not impossible, and the IPCC tells us how it could be done. It would require major changes to energy production, as well as technological and institutional changes on a pretty massive scale, though. There's no silver bullet, and what we would need is "all of the above" as long as it doesn't produce greenhouse gases: "renewables, nuclear or fossil fuels, along with carbon capture and storage, and the aggressive pursuit of energy efficiency opportunities."
The goal that this would (hopefully) achieve would be to reduce greenhouse gas emissions by 40 to 70% by 2050. And we can't wait around too much either; If we postpone action until 2030, the 2C target will be unattainable unless we can somehow remove carbon dioxide from the atmosphere fast enough to compensate.
But what about the cost of doing all this, the critics will say. Well, it looks like the costs of doing something are lower than the costs of doing nothing.
In the report, the IPCC says that action to cut greenhouse gas emissions could reduce global growth by 0.06% per year over the 21st century, leading to a "1.7% reduction in global consumption by 2030" and "3.4% by 2050 relative to a business as usual strategy." That's probably less than the impact of one of the recessions that we have every few years, and what would be the cost of a much warmer planet with an out-of-whack climate?