Climate models may underestimate future warming on tropical mountains

January 27, 2017
The Lewis glacier on Mt. Kenya has lost 90 percent over the last 75 years. New research suggests future warming on Mt. Kenya and other tropical peaks may happen much faster than climate models currently predict. Credit: Hilde Eggermont

In few places are the effects of climate change more pronounced than on tropical peaks like Mount Kilimanjaro and Mount Kenya, where centuries-old glaciers have all but melted completely away. Now, new research suggests that future warming on these peaks could be even greater than climate models currently predict.

Researchers led by a Brown University geologist reconstructed temperatures over the past 25,000 years on Mount Kenya, Africa's second-highest peak after Kilimanjaro. The work shows that as the world began rapidly warming from the last ice age around 18,000 years ago, mean annual temperatures high on the mountain increased much more quickly than in surrounding areas closer to sea level. At an elevation of 10,000 feet, mean annual temperature rose 5.5 degrees Celsius from the ice age to the pre-industrial period, the study found, compared to warming of only about 2 degrees at sea level during the same period.

"When we run state-of-the-art backward in time to this period, they underestimate the at high elevations," said James Russell, an associate professor in the Department of Earth, Environmental and Planetary Sciences and a fellow at the Institute at Brown for Environment and Society. "That implies that the models may similarly underestimate high-elevation warming in the future."

The study, which Russell led with Shannon Loomis, his former graduate student, is published in the journal Science Advances.

Temperature differences

Questions among scientists about how global warming affects tropical high elevations date back about 30 years. In 1985, influential research by Brown geologist Warren Prell showed that from the last ice age to the pre-industrial period, sea surface temperatures in the tropics rose only a degree or two. Meanwhile, temperature records estimated from high-altitude tropical glaciers suggested much more dramatic warming at high elevation.

"The climate modeling community thought there must be something wrong with one of these temperature records," Russell said, "because the models simply can't reproduce such a big difference in warming between high and low elevations."

Subsequent work has largely confirmed the estimates, but questions about the high-elevation data remained. This new study aimed to generate new, more robust high-elevation records.

Over the past decade, Russell's co-author Jaap Damsté of the University of Utrecht and colleagues have developed a new method of tracking temperature through time by studying the remains of ancient microbes. Specifically, they look at organic compounds called GDGTs that are produced in microbial cell walls. The chemical makeup of GDGTs is sensitive to temperature. In order to keep GDGTs and cell walls in a stable and permeable state, microbes alter the chemical makeup of GDGTs in response to temperature changes. Russell and his team have been able to precisely calibrate GDGT composition found in lake sediments with air temperatures through time.

Sediments from Lake Rutundu, located on the slopes of Mt. Kenya, helped researchers develop a temperature record at high elevation over the past 25,000 years. Credit: Hilde Eggermont

"We thought we could use this new temperature proxy to create a record of high-elevation temperature since the last ice age that either confirms or refutes the glacier-derived record," Russell said.

For the study, Russell and his colleagues looked at sediment cores taken from the bottom of Lake Rutundu, a volcanic lake on Mount Kenya at an elevation of around 10,000 feet. The cores preserve the signature of GDGT chemistry dating back more than 25,000 to the ice age. The data suggested that mean annual temperatures at Lake Rutundu increased about 5.5 degrees Celsius since the last ice age—a figure consistent with the previous high elevation temperature proxies. Meanwhile, temperature data from two lakes closer to sea level—Lake Tanganyika and Lake Malawi—suggest much more modest temperature changes of about 3.3 degrees and 2 degrees respectively.

Climate models are able to reproduce the temperature changes at low elevations, but they underestimate the high-elevation change by 40 percent, Russell says. That suggests there's something amiss in the way the models simulate changes in the atmospheric lapse rate—the rate at which air temperature varies with altitude.

"All climate models calculate a lapse rate—it's integral to the output of the model," Russell said. "What this work shows is that there's a problem in the way the models make that calculation."

Implications for future climate change

It's difficult to diagnose exactly what that problem is, Russell says, but it likely has something to do with the way models treat atmospheric . Water vapor content is the strongest controlling factor in governing the lapse rate (moist air cools more slowly with altitude).

"We would argue that there's probably a problem in the water vapor concentrations and therefore the feedback," Russell said.

Whatever the source of the problem, the ramifications for tropical mountains may be significant. The models miss almost half the change at in the past, and they may be underestimating future change as well.

"These are very fragile ecosystems that house extraordinary biodiversity and unique environments such as tropical glaciers," Russell said. "Our results suggest future warming in these environments could be more extreme than we predict."

Explore further: Study reveals that climate change could dramatically alter fragile mountain habitats

More information: "The tropical lapse rate steepened during the Last Glacial Maximum" Science Advances, advances.sciencemag.org/content/3/1/e1600815

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17 comments

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gkam
3.2 / 5 (11) Jan 27, 2017
The Deniers will not care, . . until the displaced people look for somewhere to go.
humy
4.6 / 5 (10) Jan 27, 2017
The only thing that would convince the climate deniers that their religion is wrong is if we are all forced by the sweltering heat to immigrate to the middle of Antarctica when, even there, we find we have need to install air-conditioning into our homes.
Even then, the deniers will not think we should do something about it (doing something about it will hit the profits of the greedy mega-rich oil companies; bad for business)
philstacy9
1.4 / 5 (10) Jan 27, 2017
Climate models may underestimate the future of scaring the public now that politics is being removed from the equation..
antigoracle
1.4 / 5 (9) Jan 27, 2017
The Deniers will not care....

The psychopath is so desperate for attention.
Show us how much you care, by telling us how much power you draw from the grid at night to power your EV and where you think that power comes from?
SamB
1.6 / 5 (11) Jan 27, 2017
Or it may over-estimate future warming on tropical mountains as it appears to be doing here. They have all scenarios covered!
It will be either warmer, cooler or somewhere in between and it appears the climate models will be correct either way.
zinger
1.4 / 5 (10) Jan 27, 2017
"Researchers led by a Brown University geologist reconstructed temperatures over the past 25,000 years on Mount Kenya"

What will all these climate researchers do when congress cuts of all their welfare that they have been living off of for too long? Maybe that degree can get them a job as a manager at McDonald's but probably not.
aksdad
2.1 / 5 (11) Jan 27, 2017
Climate models are able to reproduce the temperature changes at low elevations

In fact the climate models are NOT able to reproduce temperature changes accurately anywhere; not at low elevations nor high elevations. The IPCC AR5 report in 2013 noted the difference between measured temperatures and climate model predictions, visible in this graph here:

https://www.ipcc....S-14.jpg

By 2013 the measured temperatures were below the lowest range of predictions of the climate models and with each passing year they diverge even more. They overestimate "forcing" due to carbon dioxide and they don't take into account water vapor (clouds) which have a much greater influence on temperatures than CO2.

It should be no surprise that glaciers are still receding as they've done for the last 12,000 years since the warming that initiated the end of the last ice age.
humy
5 / 5 (7) Jan 28, 2017
The Deniers will not care....

The psychopath is so desperate for attention.
Show us how much you care, by telling us how much power you draw from the grid at night to power your EV and where you think that power comes from?

antigoracle

What you don't seem to get is that we have very little choice but to use the power REGARDLESS of where it comes from, moron.
humy
5 / 5 (8) Jan 28, 2017

It will be either warmer, cooler or somewhere in between and it appears the climate models will be correct either way.

SamB

Nope, the climate models all say it will be warmer than what it is now.
ForFreeMinds
1.4 / 5 (11) Jan 28, 2017
"Climate models may underestimate future warming on tropical mountains"

That's funny, they've all overestimated warming so far, by a lot. Al Gore said a lot of Manhatten would be under water by now. And the latest sun models predict another mini ice age coming within a decade, that could last for decades. Where's the research on the dangers of global cooling? Given history, I'd rather have warming.
humy
5 / 5 (9) Jan 28, 2017
"Climate models may underestimate future warming on tropical mountains"

That's funny, they've all overestimated warming so far, by a lot. Al Gore said a lot of Manhatten would be under water by now.

ForFreeMinds

He said nothing of the sort. He said lower Manhattan would be underwater IF and when severe ice melt occurred; which it hasn't yet. Do you comprehend the meaning of the word "IF"? Or am I going to have to explain that to you?

And the latest sun models predict another mini ice age coming within a decade, that could last for decades.

If that happens, it would be only a temporary respite from the longer term trend of man made global warming.
gkam
3.2 / 5 (9) Jan 28, 2017
Please show me where Gore said Manhattan would be underwater by now.
humy
5 / 5 (8) Jan 28, 2017
Please show me where Gore said Manhattan would be underwater by now.

He didn't. ForFreeMinds lied. See my last post.
howhot3
5 / 5 (7) Jan 28, 2017
Please show me where Gore said Manhattan would be underwater by now.
That is so typical of the climate change deniers and the rightwing goons of politics. Just make stufff up! I'm very curious to read the Al-Gore quote the goon is talking about. Good call @gkam.

Then you have the goons like @askdad who also makes up science; like.

By 2013 the measured temperatures were below the lowest range of predictions of the climate models and with each passing year they diverge even more. They overestimate "forcing" due to carbon dioxide and they don't take into account water vapor (clouds) which have a much greater influence on temperatures than CO2.
. The poor boy is confused. Globally clouds tend to cool the atmosphere with shade and increased abido, and localally it's very short term with humidity acting as an insulator on hot days but is short term. CO2 is long term, and the forcing is in the upper atmosphere. So BUZZZZZZT wrong @askdad.


humy
5 / 5 (4) Jan 29, 2017
...and they don't take into account water vapor (clouds)...

aksdad

This is just one small example out of many such examples of your many quotes which shows you obviously don't know what you are talking about;
Saying "water vapor (clouds)..." shows you think "water vapor" equates with "clouds"; it doesn't. There is water vapor in air even where there are NO clouds and even where and when there is a cloudless day even in the driest desert, moron.

HeloMenelo
5 / 5 (5) Jan 29, 2017

Askdaddy aka one of antigoracle's favorite socks always quote's the same stuff that he has no clue about, he'd do anything to look stupid on physorg to get his banana, and i must say, he's earned it...again... :D
HeloMenelo
5 / 5 (5) Jan 29, 2017
The Deniers will not care....

The psychopath is so desperate for attention.
Show us how much you care, by telling us how much power you draw from the grid at night to power your EV and where you think that power comes from?

antigoracle

What you don't seem to get is that we have very little choice but to use the power REGARDLESS of where it comes from, moron.


lol exactly well put Humy, couldn't have said it better myself, antigoracle goon once more showing his dumbsightedness in full colour :D

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