Climate scientists point to the Arctic as the place where climate change is most noticeable with dramatic sea ice loss. Photo / AP
We were warned.
On June 23, 1988, a sultry day in Washington, James Hansen told the US Congress and the world that global warming wasn't approaching - it had already arrived.
The testimony of the top Nasa scientist, said Rice University historian Douglas Brinkley, was "the opening salvo of the age of climate change."
Thirty years later, it's clear that Hansen and other doomsayers were right.
But the change has been so sweeping that it is easy to lose sight of effects large and small - some obvious, others less conspicuous.
Earth is noticeably hotter, the weather stormier and more extreme. Polar regions have lost billions of tonnes of ice; sea levels have been raised by trillions of litres of water. Far more bushfires rage.
Over 30 years - the time period climate scientists often use in their studies in order to minimise natural weather variations - the world's annual temperature has warmed 0.54C, according to the National Oceanic and Atmospheric Administration.
"The biggest change over the last 30 years, which is most of my life, is that we're no longer thinking just about the future," said Kathie Dello, a climate scientist at Oregon State University in Corvallis. "Climate change is here, it's now and it's hitting us hard from all sides."
According to an Associated Press statistical analysis of 30 years of weather, ice, fire, ocean, biological and other data, every single one of the 344 climate divisions in the Lower 48 states - NOAA groupings of US counties with similar weather - has warmed significantly, as has each of 188 cities examined.
The statistics tracking climate change since 1988 are almost numbing. North America and Europe have warmed by about 1.1C — more than any other continent. The Northern Hemisphere has warmed more than the Southern, the land faster than the ocean. Across the United States, temperature increases were most evident at night and in summer and autumn.
Since 1988, daily heat records have been broken more than 2.3 million times at weather stations across the nation, half a million times more than cold records were broken.
AP interviewed more than 50 scientists who confirmed the depth and spread of warming.
Clara Deser, climate analysis chief at the National Centre for Atmospheric Research, said that when dealing with 30-year time periods in smaller regions than continents or the globe as a whole, it would be unwise to say all the warming is man-made. Her studies show that in some places in North America - though not most - natural weather variability could account for as much as half of local warming.
But when you look at the globe as a whole, especially since 1970, nearly all the warming is man-made, said Zeke Hausfather of the independent science group Berkeley Earth. Without extra carbon dioxide and other greenhouse gases, he said, the Earth would be slightly cooling from a weakening sun.
Numerous scientific studies and government reports calculate that greenhouse gases in the big picture account for more than 90 per cent of post-industrial Earth's warming.
"It would take centuries to a millennium to accomplish that kind of change with natural causes. This, in that context, is a dizzying pace," said Kim Cobb, a climate scientist at Georgia Tech in Atlanta.
Since the 1800s scientists have demonstrated that certain gases in Earth's atmosphere trap heat from the sun like a blanket. Human activities such as burning of coal, oil and gasoline are releasing more of those gases into the atmosphere, especially carbon dioxide. US and international science reports say that more than 90 per cent of the warming that has happened since 1950 is man-made.
Others cautioned that what might seem to be small increases in temperature should not be taken lightly.
"One or two degrees may not sound like much, but raising your thermostat by just that amount will make a noticeable effect on your comfort," said Deke Arndt, NOAA's climate monitoring chief in Asheville, North Carolina, which has warmed nearly 0.98C in 30 years.
Arndt said average temperatures don't tell the entire story: "It's the extremes that these changes bring." The nation's extreme weather — flood-inducing downpours, extended droughts, heatwaves and bitter cold and snow — has doubled in 30 years, according to a federal index.
The northeast's extreme rainfall has more than doubled. Brockton, Massachusetts, had only one day with at least 101mm of rain from 1957 to 1988, but a dozen of them in the 30 years since, according to NOAA records.
Ellicott City, Maryland, just had its second thousand-year flood in little less than two years. And the summer's named Atlantic storms? On average, the first one now forms nearly a month earlier than it did in 1988, according to University of Miami hurricane researcher Brian McNoldy.
The 14 costliest hurricanes in American history, adjusted for inflation, have hit since 1988, reflecting both growing coastal development and a span that included the most intense Atlantic storms on record.
"The collective damage done by Atlantic hurricanes in 2017 was well more than half of the entire budget of our Department of Defence," said MIT's Kerry Emanuel.
Climate scientists point to the Arctic as the place where climate change is most noticeable with dramatic sea ice loss, a melting Greenland ice sheet, receding glaciers and thawing permafrost. The Arctic has warmed twice as fast as the rest of the world.
It is disappearing 50 years faster than scientists predicted, said Michael Mann, a climate scientist at Pennsylvania State University.
"There is a new Arctic now because the Arctic Ocean is now navigable" at times in the summer, said Mark Serreze, director of the National Snow and Ice Data Center.
The vast majority of glaciers around the world have shrunk. A Nasa satellite that measures shifts in gravity calculated that Earth's glaciers lost 279 billion tonnes of ice — nearly 253 trillion litres of water — from 2002 to 2017.
In 1986, the Begich Boggs visitor centre at Alaska's Chugach National Forest opened to highlight the Portage glacier. But the glacier keeps shrinking.
"You absolutely cannot see it from the visitor centre and you haven't in the last 15 or so years," said climatologist Brian Brettschneider of the University of Alaska Fairbanks.
Ice sheets in Greenland and West Antarctica have also shrivelled, melting about 412 billion tonnes of ice into water, according to the Nasa satellite. That's enough to cover the state of Georgia in water nearly three metres deep. And it is enough — coupled with all the other melting ice — to raise the level of the seas. Overall, Nasa satellites have shown three inches of sea level rise (75mm) in just the past 25 years.
With more than 70 per cent of the Earth covered by oceans, a 3-inch increase means about 6500 cubic miles (27,150 cu km) of extra water. That's enough to cover the entire United States with water about three metres deep. It's a fitting metaphor for climate change, say scientists: We're in deep, and getting deeper.
"Thirty years ago, we may have seen this coming as a train in the distance," NOAA's Arndt said. "The train is in our living room now."
- AP
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