Kate Marvel writes:

Two and a half years ago, when I was asked to help write the most authoritative report on climate change in the United States, I hesitated. Did we really need another warning of the dire consequences of climate change in this country? The answer, legally, was yes: Congress mandates that the National Climate Assessment be updated every four years or so. But after four previous assessments and six United Nations reports since 1990, I was skeptical that what we needed to address climate change was yet another report.

In the end, I said yes, but reluctantly. Frankly, I was sick of admonishing people about how bad things could get. Scientists have raised the alarm over and over again, and still the temperature rises. Extreme events like heat waves, floods and droughts are becoming more severe and frequent, exactly as we predicted they would. We were proved right. It didn’t seem to matter.

Our report, which was released on Tuesday, contains more dire warnings. There are plenty of new reasons for despair. Thanks to recent scientific advances, we can now link climate change to specific extreme weather disasters, and we have a better understanding of how the feedback loops in the climate system can make warming even worse. We can also now more confidently forecast catastrophic outcomes if global emissions continue on their current trajectory. But to me, the most surprising new finding in the Fifth National Climate Assessment is this: There has been genuine progress, too.

I’m used to mind-boggling numbers, and there are many of them in this report. Human beings have put about 1.6 trillion tons of carbon in the atmosphere since the Industrial Revolution — more than the weight of every living thing on Earth combined. But as we wrote the report, I learned other, even more mind-boggling numbers. In the last decade, the cost of wind energy has declined by 70 percent and solar has declined 90 percent. Renewables now make up 80 percent of new electricity generation capacity. Our country’s greenhouse gas emissions are falling, even as our G.D.P. and population grow. [Continue reading…]