One of the central challenges of climate change is that it isn’t easily undone. Global warming isn’t like a fire in your fireplace, with heat that will dissipate when you stop feeding it. It is better compared to piling on more and winter coats and hats and blankets. The more you put on, the hotter you get and the hotter you stay.

The effect of this, particularly with atmospheric carbon dioxide, is that the current warming that the Earth is experiencing is the cumulative effect of well over a century of burning fossil fuels. Carbon dioxide from a 1920 Pittsburgh coke oven fire is still up there, absorbing a bit of heat energy and occasionally bouncing it back to the ground.

But this does not mean that the warming we’re currently experiencing is largely due to emissions a century ago. Instead, data from the Global Carbon Project (GCP) shows how the cumulative amount of emissions has surged in the past few decades. Half of all carbon dioxide emissions included in the GCP’s estimates have occurred since 1991. Since the release of Al Gore’s “An Inconvenient Truth” in 2006, cumulative global emissions have increased by about 40 percent.

No country has contributed to those emissions as much as the United States has, though China has added more in recent years. If we narrow the window we’re considering to the past decade, we see that cumulative global emissions have jumped more than 26 percent, with the United States’ total increasing by about 15 percent. China’s emissions, though, have increased 74 percent.

This is why, for years, American climate activists and politicians focused on the issue they have argued for the need to take a global approach to the issue. Were the United States to eliminate all emissions, it wouldn’t matter much if China and India increased emissions to replace them. This is in part why the Obama administration’s 2014 agreement with China on climate change and the agreement reached in Glasgow this month are important: They indicate a mutual commitment to the issue.

The challenge for activists domestically is that even as climate change has become increasingly apparent in extreme weather events and droughts, and even as the United States has continued to push carbon dioxide and other greenhouse gases such as methane into the atmosphere, support for regulating those emissions has fallen. Polling from The Post and ABC News released this week found that Americans were less supportive of regulation than they were in 2012. The drop was most pronounced among Republicans.

This is because climate change was rolled into the broader partisan culture war. Climate change became a deeply polarized issue, in part because it is often framed as pitting the environment against jobs (despite the growth in renewable-energy employment) and as increasing consumer costs (despite the decline in relative prices for electricity). It’s also because many opponents have positioned the pro-climate position as being anti-freedom, in a bit of rhetoric that will be familiar to those watching the politicization of the coronavirus pandemic.

Regulation is not the only tool available for addressing emissions, and, in fact, emissions in the United States have been reduced without federal legislation. But, as The Washington Post’s Darryl Fears and Emily Guskin reported on Friday, the polling shift isn’t only about regulation. Since we last polled in 2015, the percentage of Republicans expressing concern about climate change has also fallen.

We are adding greenhouse gases to the atmosphere at a slower rate than we used to, but we’re still adding them. So is the rest of the world, at a pace that scientists suggest will have long-term negative consequences. And meanwhile, American voters are less likely now to support federal action than they were 286 billion metric tons of carbon-dioxide equivalent emissions ago.