By 2047, Coldest Years May Be Warmer Than Hottest in Past, Scientists Say
If greenhouse emissions continue their
steady escalation, temperatures across
most of the earth will rise to levels with
no recorded precedent by the middle of
this century, researchers said
Wednesday.
Scientists from the University of
Hawaii at Manoa calculated that by
2047, plus or minus five years, the
average temperatures in each year will
be hotter across most parts of the
planet than they had been at those
locations in any year between 1860
and 2005.
To put it another way, for a given
geographic area, “the coldest year in
the future will be warmer than the
hottest year in the past,” said Camilo
Mora , the lead scientist on a paper
published in the journal Nature.
Unprecedented climates will arrive
even sooner in the tropics, Dr. Mora’s
group predicts, putting increasing stress
on human societies there, on the coral
reefs that supply millions of people
with fish, and on the world’s greatest
forests.
“Go back in your life to think about the
hottest, most traumatic event you have
experienced,” Dr. Mora said in an
interview. “What we’re saying is that
very soon, that event is going to
become the norm.”
The research comes with caveats. It is
based on climate models , huge
computer programs that attempt to
reproduce the physics of the climate
system and forecast the future response
to greenhouse gases. Though they are
the best tools available, these models
contain acknowledged problems, and
no one is sure how accurate they will
prove to be at peering many decades
ahead.
The models show that unprecedented
temperatures could be delayed by 20 to
25 years if there is a vigorous global
effort to bring emissions under control.
While that may not sound like many
years, the scientists said the emissions
cuts would buy critical time for nature
and for human society to adapt, as well
as for development of technologies that
might help further reduce emissions.
Other scientists not involved in the
research said that slowing emissions
would have a bigger effect in the long
run, lowering the risk that the climate
would reach a point that triggers
catastrophic changes. They praised the
paper as a fresh way of presenting
information that is known to specialists
in the field, but not by the larger
public.
“If current trends in carbon dioxide
emissions continue, we will be pushing
most of the ecosystems of the world
into climatic conditions that they have
not experienced for many millions of
years,” said Ken Caldeira, a climate
researcher at the Carnegie Institution
for Science in Stanford, Calif.
The Mora paper is a rarity: a class
project that turned into a high-profile
article in one of the world’s most
prestigious scientific journals.
Dr. Mora is not a climate scientist;
rather he is a specialist in using large
sets of data to illuminate
environmental issues. He assigned a
class of graduate students to analyze
forecasts produced by 39 of the world’s
foremost climate models. The models,
whose results are publicly available,
are operated by 21 research centers in
12 countries, and financed largely by
governments.
Thousands of scientific papers have
been published about the model results,
but the students identified one area of
analysis that was missing. The results
are usually reported as average
temperature changes across the planet.
But that gives little sense of how the
temperature changes in specific places
might compare with historical norms.
“We wanted to give people a really
relatable way to understand climate,”
said Abby G. Frazier, a doctoral
candidate in geography.
So Dr. Mora and his students divided
the earth into a grid, with each cell
representing 386 square miles.
Averaging the results from the 39
climate models, they calculated a date
they called “climate departure” for
each location — the date after which all
future years were predicted to be
warmer than any year in the historical
record for that spot on the globe.
The results suggest that if emissions of
greenhouse gases remain high, then
after 2047, more than half the earth’s
surface will experience annual
climates hotter than anything that
occurred between 1860 and 2005, the
years for which historical temperature
data and reconstructions are available.
If assiduous efforts were made to bring
emissions down, that date could be
pushed back to 2069, the analysis
found.
With the technique the Mora group
used, it is possible to specify climate
departure dates for individual cities.
Under high emissions, climate
departure for New York City will come
in 2047, the paper found, plus or minus
the five-year margin of error. But
lower emissions would push that to
2072.
For Beijing, climate departure would
come in 2046 under high emissions, or
2078 under lower emissions. The dates
for Moscow are 2063 and 2092; for
Washington, 2047 and 2071.
Perhaps the most striking findings are
in the tropics. Climate variability there
is much smaller than in high latitudes,
and the extra heat being trapped by
greenhouse gases will push the
temperature beyond historical bounds
much sooner, the research found.
Under high emissions, the paper found
a climate departure date of 2031 for
Mexico City, 2029 for Jakarta and for
Lagos, Nigeria, and 2033 for Bogotá,
Colombia.
Many people perceive climate change
to be most serious at the poles, and the
largest absolute changes in temperature
are already occurring in the Arctic and
parts of Antarctica. But the Mora paper
dovetails with previous research
suggesting that the biggest risks to
nature and to human society, at least in
the near term, may actually be in the
tropics.
People living in the tropics are
generally poor, with less money to
adapt to climate change than people in
the mid-latitude rich countries that are
burning the most carbon-based fuels
and contributing most of the emissions.
Plants and animals in the tropics also
are accustomed to a narrow
temperature range. Organisms that do
not have the genetic capacity to adapt
to rapid climatic changes will be forced
to move, or will be driven to extinction,
climate scientists say.
“I am certain there will be massive
biological and social consequences,” Dr.
Mora said. “The specifics, I cannot tell
you.”
