By Tim Radford

The probable changes as the world heats are so great that climate adaptation to cope with the inevitable is now essential, scientists are warning.

Forest damage, drought and floods, for example, will all worsen, and tidal ranges are already changing. More than half of all the natural vegetation of California is at risk as temperatures rise.

Even were the U.S. and other nations to honor the promises made in the Paris agreement of 2015, one fourth of California's natural wilderness would be under stress from global warming, a new study shows.

And on top of temperature rise, California is increasingly at risk from severe drought, says a different study. U.S. government scientists believe they have established a link between the retreat of Arctic sea ice and a decline in rainfall in the Golden State.

Drought and Flood

And while California becomes ever more parched, its forests at ever-greater risk of insect attack and wildfire, 43 other U.S. states face a dramatic increase in flood hazard, with a tenfold rise in the numbers of people at risk from the worst river floods.

And—although President Trump has dismissed climate change as a hoax and announced a withdrawal from the Paris agreement to limit the use of fossil fuels—the tide gauges of the Chesapeake and Delaware Bays on the East Coast of the U.S. tell a different story. They confirm that climate change has already begun to affect high and low water tides.

U.S. researchers report in the journal Ecosphere that they looked at the consequences for California if global greenhouse gas emissions continue at their present rate, to go on fueling global warming.

They mapped 30 different vegetation types—California's canopy includes a huge variety of mountain conifer, forest coastal woodland, upland sagebrush scrub, grassland and so on—and considered nine climate and precipitation variables, and then looked at computer models of future global warming, which predict, at worst, a global average rise of 4.5 C by 2100.

"At current rates of emissions, about 45-56 C of all the natural vegetation in the state is at risk, or from 61,190 to 75,866 square miles," said James Thorne of the University of California Davis, who led the study.

"If we reduce the rate to Paris Accord targets, those numbers are lowered to between 21 and 28% of the lands at climatic risk." The research measures only the impact of climate change: not of the accompanying hazards.

During the 2012-2016 Californian drought—the worst on record—more than 127 million trees died of insect infestation, and wildfire devastated huge tracts of forest and scrub.

And according to researchers at Lawrence Livermore National Laboratory, more drought could be on the way. They report in Nature Communications that the steady attrition of sea ice in the Arctic Ocean triggers a change in atmospheric convection over the tropical Pacific, which creates the right conditions for an atmospheric ridge over the North Pacific, which means California gets a lot sunnier, and therefore drier.

Rising Rivers

"On average, considering a 20-year mean, we find a 10-15 percent decrease in California's rainfall. However some individual years could become much drier, and others wetter," said Ivana Cvijanovic, who led the research. "The recent California drought appears to be a good illustration of what sea ice-driven precipitation decline should look like."

Elsewhere in the U.S., drought may not be the big problem. German researchers report in the journal Science Advances that they calculated the necessary increase in flood protection over the next 25 years worldwide, as the planet warms.

They looked not just at individual countries but at cities too, to calculate the numbers at hazard of rising rivers, including Europe.

In Germany, the numbers at risk from the worst 10 percent of all floods will rise sevenfold. In North America, the increase will be tenfold. In the U.S. 43 states could see more damage from the worst floods.

Risk Is Greatest in Asia

The overall numbers at risk are greatest in Asia—70 million people now, and 156 million by 2040. The scientists make the case that governments need to think about adaptation. The surprise was that even the most developed nations would be affected.

"The findings should be a warning to decision-makers," said Anders Levermann, of the Potsdam Institute for Climate Impact Research, and one of the authors. "If they choose to ignore the issue, sadly enough disaster will come."

"The time has come where mitigating future climate change must be accompanied by adapting to the climate change we have already caused. Doing nothing will be dangerous."

And the impact of climate change so far is now backed up by evidence in the Journal of Geophysical Research. Once again, the research is driven by a concern to identify future sources of flooding or erosion.

Shifting Tides

Oceanographers built a computer model based on a century of measurements of the tides at 15 locations in the Chesapeake and Delaware Bays on the U.S. Eastern Coast. Overall, by 2100, sea levels could rise by as much as a meter.

They found evidence that sea level rise so far has already begun to change the ranges of low and high tides—in some cases by up to 20 percent—which in turn are governed by the contours of the two great river estuaries.

"In the Delaware Bay, as you go upstream toward Philadelphia, the shore lines are converging in a kind of funnel shape, and so we see that amplifies sea level rise's effects on the tides," said Andrew Ross, a meteorologist then at Penn State University, but now at Princeton. "That amplification gets magnified the farther you go upstream."

Reposted with permission from our media associate Climate News Network.