When it comes to climate change, did we accurately predict in 2000 what would be happening now?
"What the models correctly told us 20 years ago is that if we continued to add fossil fuels at an increasing rate to the atmosphere, we'd see an increasing range of consequences, including a decline in Arctic sea ice, a rise in sea levels and shifts in precipitation patterns," Weather Underground meteorologist Robert Henson told USA TODAY.
Overall, we're running quite close to the projections made in 2000 for carbon dioxide concentration, global temperature and sea level, Henson said.
Here's a look at climate change indicators for 2020:
Carbon dioxide is the greenhouse gas that scientists say is most responsible for global warming.
Since the early 1990s, the carbon dioxide level in the Earth's atmosphere has jumped from about 358 parts per million to nearly 412 ppm, according to the National Oceanic and Atmospheric Administration. That’s a 15% rise in 27 years.
Since 1992, the global sea level has risen on average 2.9 millimeters a year. That’s a total of 78.3 millimeters, according to NOAA.
Penn State University meteorologist Michael Mann argued that we underestimated the rate of ice sheet collapse, which has "implications for future sea-level rise."
Both of the world's giant ice sheets have lost tremendous amounts of ice in the past two to three decades: The Greenland ice sheet lost 5.2 trillion tons of ice from 1993 to 2018, according to a study in the Proceedings of the National Academy of Sciences.
The Antarctic ice sheet lost 3 trillion tons of ice from 1992 to 2017, according to a study in the journal Nature.
Mann told USA TODAY that we "underestimated the dramatic increase in persistent weather extremes like the unprecedented heat waves, droughts, wildfires and floods we’ve witnessed in recent years."
Since 1993, there have been 212 weather disasters that cost the United States at least $1 billion each, when adjusted for inflation.
In total, they cost $1.45 trillion and killed more than 10,000 people. That’s an average of 7.8 such disasters per year since 1993, compared with 3.2 per year from 1980 to 1992, according to NOAA.
"Just as climate models almost certainly underestimate the impact climate change has already had on such weather extremes, projections from these models also likely underestimate future increases in these types of events," Mann wrote in The Washington Post last year.
“By and large, our models have gotten it right, plus or minus a little bit,” said Zeke Hausfather, a University of California-Berkeley scientist.
Global temps rising
Henson noted it's clear that global climate models were on the right track 20 years ago: Global temperatures would continue to rise as greenhouse gases continued to accumulate in the atmosphere.
That's been borne out: The global average temperature rose a tad more than a degree Fahrenheit since the mid-'90s, according to NOAA.
"The global temperature projections were just about on the money," Mann said.
These climate models weren't designed to predict decade-by-decade variability, Henson said, so we didn't fully anticipate the slowdown in global atmospheric warming in the first decade of this century and the much more rapid increase in the 2010s, both of which were linked to the evolving rate of heat storage in the ocean.
The annual average extent of Arctic sea ice has shrunk from 4.7 million square miles in 1992 to 3.9 million square miles in 2019, according to the National Snow and Ice Data Center. That’s a 17% decrease.
Droughts and wildfires
"Another thing beyond the scope of year-2000 outlooks were some aspects of regional climate change," Henson said. "For example, it's now clear that droughts in California are much more likely to be 'hot' droughts, and this has laid the groundwork for longer, more devastating wildfire seasons."
The number of acres burned by wildfires in the USA has more than doubled from a five-year average of 3.3 million acres in the 1990s to 7.6 million acres in 2018, the National Interagency Fire Center said.
'Sunny day' flooding
"We're also appreciating the threat posed by 'sunny day' flooding much more than we did in 2000," Henson said. "Tidal flooding is far more frequent on many parts of the Gulf and Atlantic coast than it was 20 years ago, and NOAA has projected that some locations could see more than 80 flood days a year as soon as the 2040s."