September 27, 2013 — 95%. That’s how certain the hundreds of scientists who contribute to the Intergovernmental Panel on Climate Change (IPCC), which released the first chapter of its fifth assessment on global warming this morning, are that human beings are the “dominant cause of observed warming” that’s been seen since the mid-20th century.
In science, which almost always speaks in probabilities, that’s about as clear as you get. This is not news—while the certainty around the scientific case for man-made climate change has tightened somewhat, much of the new report reiterates the conclusions reached in the last IPCC assessment,which was released in 2007. But while the broad conclusions of the science may not have changed that much, the political environment into which the report is being released has changed significantly. Or perhaps better—it hasn’t changed that much. The scientific case for taking action to reduce greenhouse gas emissions and prepare for the effects of climate change remains clear, despite nagging doubts about the fact that global temperatures have risen more slowly in recent years despite the continued increase in carbon emissions. But exactly what and how much action should be taken, and how politicians should balance tomorrow’s threat of climate change against any number of present day challenges, is something that won’t be answered by another thick sheaf of scientific reports.
Which isn’t to say that the scientists aren’t trying. Going beyond the conclusions seen in the last four assessments, which date back to the early 1990s, this year the IPCC formally endorsed a “carbon budget”—a red line for the amount of carbon dioxide, created chiefly by burning fossil fuels and through deforestation, that can be emitted without warming increasing beyond an internationally agreed target of 3.6 F (2 C). Think of it as a speed limit for the global economy—emit more than one trillion tons of carbon, and we’ll likely be in the red. That should be worrying, given the fact that there are 3 trillion tons of carbon left in the ground, and as I wrote in TIME this week, energy companies are developing new technologies, like hydrofracking and directional drilling, that are enabling them to find fossil fuels that were long considered uneconomical.
Read the full story and watch the video at Time Magazine