This, after all, is the reason the climate crisis has become an existential threat to the future of human civilization. Last April, the average CO2 concentrations in the Earth's atmosphere exceeded 400 parts-per-million on a sustained basis for the first time in at least 800,000 years and probably for the first time in at least 4.5 million years (a period that was considerably warmer than at present).
According to a cautious analysis by the influential climate scientist James Hansen, the accumulated man-made global-warming pollution already built up in the Earth's atmosphere now traps as much extra heat energy every day as would be released by the explosion of 400,000 Hiroshima-class nuclear bombs. It's a big planet, but that's a lot of energy.
And it is that heat energy that is giving the Earth a fever. Denialists hate the "fever" metaphor, but as the American Association for the Advancement of Science (AAAS) pointed out this year, "Just as a 1.4degree-fever change would be seen as significant in a child's body, a similar change in our Earth's temperature is also a concern for human society."
Thirteen of the 14 hottest years ever measured with instruments have occurred in this century. This is the 37th year in a row that has been hotter than the 20th-century average. April was the 350th month in a row hotter than the average in the preceding century. The past decade was by far the warmest decade ever measured.
Many scientists expect the coming year could break all of these records by a fair margin because of the extra boost from the anticipated El Niño now gathering in the waters of the eastern Pacific. (The effects of periodic El Niño events are likely to become stronger because of global warming, and this one is projected by many scientists to be stronger than average, perhaps on the scale of the epic El Niño of 1997 to 1998.)
The fast-growing number of extreme-weather events, connected to the climate crisis, has already had a powerful impact on public attitudes toward global warming. A clear majority of Americans now acknowledge that man-made pollution is responsible. As the storms, floods, mudslides, droughts, fires and other catastrophes become ever more destructive, the arcane discussions over how much of their extra-destructive force should be attributed to global warming have become largely irrelevant. The public at large feels it viscerally now. As Bob Dylan sang, "You don't need a weatherman to know which way the wind blows."
Besides, there is a simple difference between linear cause and effect and systemic cause and effect. As one of the world's most-respected atmospheric scientists, Kevin Trenberth, has said, "The environment in which all storms form has changed owing to human activities."
For example, when Supertyphoon Haiyan crossed the Pacific toward the Philippines last fall, the storm gained strength across seas that were 5.4 degrees Fahrenheit warmer than they used to be because of greenhousegas pollution. As a result, Haiyan went from being merely strong to being the most powerful and destructive ocean-based storm on record to make landfall. Four million people were displaced (more than twice as many as by the Indian Ocean tsunami of 10 years ago), and there are still more than 2 million Haiyan refugees desperately trying to rebuild their lives.
When Superstorm Sandy traversed the areas of the Atlantic Ocean windward of New York and New Jersey in 2012, the water temperature was nine degrees Fahrenheit warmer than normal. The extra convection energy in those waters fed the storm and made the winds stronger than they would otherwise have been. Moreover, the sea level was higher than it used to be, elevated by the melting of ice in the frozen regions of the Earth and the expanded volume of warmer ocean waters.
Five years earlier, denialists accused me of demagogic exaggeration in an animated scene in my documentary An Inconvenient Truth that showed the waters of the Atlantic Ocean flooding into the 9/11 Ground Zero Memorial site. But in Sandy's wake, the Atlantic did in fact flood Ground Zero – many years before scientists had expected that to occur.
Similarly, the inundation of Miami Beach by rising sea levels has now begun, and freshwater aquifers in low-lying areas from South Florida to the Nile Delta to Bangladesh to Indochina are being invaded by saltwater pushed upward by rising oceans. And of course, many low-lying islands – not least in the Bay of Bengal – are in danger of disappearing altogether. Where will the climate refugees go? Similarly, the continued melting of mountain glaciers and snowpacks is, according to the best scientists, already "affecting water supplies for as many as a billion people around the world."
Just as the extreme-weather events we are now experiencing are exactly the kind that were predicted by scientists decades ago, the scientific community is now projecting far worse extreme-weather events in the years to come. Eighty percent of the warming in the past 150 years (since the burning of carbon-based fuels gained momentum) has occurred in the past few decades. And it is worth noting that the previous scientific projections consistently low-balled the extent of the globalwarming consequences that later took place – for a variety of reasons rooted in the culture of science that favor conservative estimates of future effects.
In an effort to avoid these cultural biases, the AAAS noted this year that not only are the impacts of the climate crisis "very likely to become worse over the next 10 to 20 years and beyond," but "there is a possibility that temperatures will rise much higher and impacts will be much worse than expected. Moreover, as global temperature rises, the risk increases that one or more important parts of the Earth's climate system will experience changes that may be abrupt, unpredictable and potentially irreversible, causing large damages and high costs."
Just weeks after that report, there was shock and, for some, a temptation to despair when the startling news was released in May by scientists at both NASA and the University of Washington that the long-feared "collapse" of a portion of the West Antarctic ice sheet is not only under way but is also now "irreversible." Even as some labored to understand what the word "collapse" implied about the suddenness with which this catastrophe will ultimately unfold, it was the word "irreversible" that had a deeper impact on the collective psyche.
Just as scientists 200 years ago could not comprehend the idea that species had once lived on Earth and had subsequently become extinct, and just as some people still find it hard to accept the fact that human beings have become a sufficiently powerful force of nature to reshape the ecological system of our planet, many – including some who had long since accepted the truth about global warming – had difficulty coming to grips with the stark new reality that one of the long-feared "tipping points" had been crossed. And that, as a result, no matter what we do, sea levels will rise by at least an additional three feet.
The uncertainty about how long the process will take (some of the best ice scientists warn that a rise of 10 feet in this century cannot be ruled out) did not change the irreversibility of the forces that we have set in motion. But as Eric Rignot, the lead author of the NASA study, pointed out in The Guardian, it's still imperative that we take action: "Controlling climate warming may ultimately make a difference not only about how fast West Antarctic ice will melt to sea, but also whether other parts of Antarctica will take their turn."
The news about the irreversible collapse in West Antarctica caused some to almost forget that only two months earlier, a similar startling announcement had been made about the Greenland ice sheet. Scientists found that the northeastern part of Greenland – long thought to be resistant to melting – has in fact been losing more than 10 billion tons of ice per year for the past decade, making 100 percent of Greenland unstable and likely, as with West Antarctica, to contribute to significantly more sea-level rise than scientists had previously thought.
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