Tropics hit earliest by climate change

"What's past is prologue" – William Shakespeare, The Tempest

Upwards of 5 billion people in the tropics will soon find temperature and other weather conditions falling outside anything experienced in modern record-keeping, according to a groundbreaking study published Wednesday.

The study, by a team of University of Hawaii researchers led by professor Camilo Mora, is the first to map the timing of "climate departures" – when a particular region's climate conditions escape the bounds recorded over the past 140-odd years by modern instruments.

Among the team's surprising findings: The tropics will depart first, even though all climate models and data show the Arctic is warming fastest. And the transformation, underway now, will happen very quickly.

"We didn't anticipate that these timings were going to be that early," Mora said in an interview. 

"The tropics are going to be the most vulnerable," he added. "The reason for that? They're adapted to the narrowest range."

The finding, experts note, also has broad ramifications for wildlife and biodiversity. The study was published by the journal Nature.

The Mora lab's analysis shows that 1 billion people will find their local climate outside historic norms starting as early as 2020, even if stringent emissions curbs are in place. Without curbs, some 5.5 billion people worldwide will find their homes outside climate norms within 50 years.

Plot those findings against economic data, Mora said, and the situation grows dire: The regions facing the impacts first – southeast Asia, much of sub-Sahara Africa – have the least economic ability to respond.

Stuart Pimm, professor of conservation ecology at Duke University, called the findings astonishing and turned to Shakespeare's famous line in The Tempest for perspective.

"What's past is no longer prologue," he said. "We are outside of our experience."

Counterintuitive results

The results are counterintuitive. While the globe has warmed an average of 0.9 degrees Celsius (1.4ºF) over the past century, the warming has not been even: The Arctic has warmed twice as much over that period, scientists say, and melting ice and polar bears have become the face of climate impacts.

But the Arctic experiences wild temperature swings. Species – and humans – there are adapted to a broader climate band. Thus, said Mora, the region needs a bigger temperature swing to depart its climate history: Anchorage, for instance, won't escape today's climate norm until closer to the 2070s, according to the Mora lab's data.

Life in the tropics, however, is accustomed to a far narrower band, Mora said. So while the temperature change may be smaller than what's seen in the Arctic, the impact is keener: Manokwari, a city of 130,000 in West Papua, Indonesia, will be the first in the globe to depart its climate, heading into uncharted waters for good by 2020, Mora's data show.

Those changes, the paper's authors cautioned, are already underway: "We emphasise that although our index commonly identifies future dates," they wrote, "this does not imply that climate change is not already occurring."

The impact to the tropics could be considerable, Mora and other ecologists say: The tropics shelter the globe's most diverse, complex ecosystems. 

"These changes are on an absolute scale very small, but they will easily exceed what these species can tolerate," Mora said.

One million maps

Mora is a data analyst, not a climate modeler. Analysing global climate data as a lab exercise, his team noticed a paucity of information on the timing of climate change.

But unlocking that information proved tricky: Mora's lab analysed one million maps, charting more than 50,000 locations on each map. Those were then combined with climate, economic and ecology data, including information on more than 300,000 species "just to get the general picture", Mora said.

For Mora, the most surprising finding was that sharp emissions curbs only bought society 20 years before the tropics started to depart their climate.

The Mora team used two different emissions scenarios – or 'forcings' – to chart the onset of departure: One assuming 'business as usual', the other assuming widespread, expensive and draconian cuts to greenhouse gas emissions.

"The biggest shock of all is that under both scenarios we will exceed historical records," he said. 

Policy questions

That, he noted, opens a host of policy questions: If this is going to happen no matter what, why make costly sacrifices just to push the date 20 years in the future?

Mora answers that with an analogy. If you're on the highway, approaching an accident, your first reaction, he said, is to hit the brake. "It's very certain you're not going to put your foot on the gas."

Buying time – even just 20 years – is important given the lack of resources available to countries most impacted, he said. "We're facing these unprecedented climates very, very early. We just don't have the economic capacity to face these changes."

Stay on the ladder

Another unanswerable question facing ecologists, modelers and analysts like Mora is what specific impacts confront society as the climate departs.

Mora again turns to an analogy, this time of a ladder: If you're three flights up on a ladder and fall, you will get hurt, he said. But will you break your nose, your arm or your leg? No one can say, given the many unknowns encountered on the way down.

If you had those specifics, of course, you could pad your elbow or knee or take precautions, he said.

"But maybe, if you only know generalities, maybe you should focus on not falling off the ladder."

Douglas Fischer is editor of The Daily Climate, an independent, foundation-funded news service covering climate change, energy and the environment. 

Graphics showing climate departure courtesy Nature and the Mora Lab. 

This article was originally published by The Daily Climate. Republished with permission.