More than half of the carbon dioxide spewed into the atmosphere by the burning of fossil fuels has been exhaled during the past three decades.

Since 1989, human activity has emitted 820 gigatons — a gigaton is equal to a billion metric tons, a metric ton is 2,205 pounds — of carbon dioxide from the use of fossil fuels. Our carbon emissions total since 1751 is 1,578 gigatons, according to the Carbon Dioxide Information Analysis Center at the Oak Ridge National Laboratory.

In 1992, the United Nations ratified its climate-change framework, establishing a scientific consensus that prioritized the stabilization of greenhouse-gas concentrations “at a level that would prevent dangerous anthropogenic (human induced) interference with the climate system.”

This means, as David Wallace-Wells writes in his 2019 book The Uninhabitable Earth: Life After Warming, humans have “now engineered as much ruin knowingly as we ever managed in ignorance.”

That fact should hit us like a Muhammad Ali uppercut to the jaw. We should be staggering, our knees wobbling.

But you know what? We, collectively, don’t care.

Five years ago we learned that Exxon was aware of climate change as early as 1977. In the 1980s, both Exxon and Shell carried out internal assessments of the carbon dioxide released by fossil fuels, and forecast the planetary consequences of these emissions.

Yet, many of us still falsely label the climate crisis a “Chinese hoax.” Many of us believe it’s a scheme concocted by climate scientists to get rich. Some of us blame the wildfires raging in Australia on arsonists, and even if that were true, we ignore the fact that the wildfires there, here, and everywhere are burning faster, bigger, and longer because of all the climate-changing greenhouse gases we have been relentlessly pumping into the atmosphere since the Industrial Revolution.

We pay no mind to melting Arctic ice because we don’t care if all the polar bears die. But we fail, collectively, to realize that less ice means less sunlight is reflected away from us and more is baked in to a steadily warming planet.

The oceans are absorbing much of this excess heat and accumulating greenhouse gases. They’re becoming acidified. The diversity of life they support is dwindling. Essentially, the planet’s lungs are beginning to fail. We shrug our collective shoulders. Local elected officials say there’s nothing we can do. The Department of Justice works closely with the fossil-fuel industry to oppose climate lawsuits. The Department of Homeland Security lists environmental activists engaged in non-violent civil disobedience targeting the fossil-fuel industry as “extremists” and lists some of the activists alongside white nationalists and mass killers.

Besides altering ocean chemistry, in a manner that does little to promote human existence, and melting sea ice, our increasingly warming planet is also thawing Arctic permafrost, which, according to the National Aeronautics and Space Administration, contains 1.8 trillion tons of carbon — more than twice as much as is currently suspended in Earth’s atmosphere.

The longer we allow this negative feedback loop to grow and intensify, the bleaker the future we leave for our descendants. The longer we deny reality, the less we leave behind for our children and grandchildren.

Frank Carini is the editor of ecoRI News. This column originally appeared in The Valley Breeze as a guest opinion.