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Finally! The Greenland deglaciation paradox sorted.

from ScienceDaily

Bo Vinther prepares an ice core for visual inspection. Credit: Photograph by Christian Morel

A new study of three ice cores from Greenland documents the warming of the large ice sheet at the end of the last ice age — resolving a long-standing paradox over when that warming occurred.

 Large ice sheets covered North America and northern Europe some 20,000 years ago during the coldest part of the ice age, when global average temperatures were about four degrees Celsius (or seven degrees Fahrenheit) colder than during pre-industrial times. And then changes in Earth’s orbit around the sun increased the solar energy reaching Greenland. Beginning some 18,000 years ago, release of carbon from the deep ocean led to a graduate rise in atmospheric carbon dioxide (CO2).

Yet past analysis of ice cores from Greenland did not show any warming response as would be expected from an increase in CO2 and solar energy flux, the researchers note.

In this new study, funded by the National Science Foundation and published this week in the journal Science, scientists reconstructed air temperatures by examining ratios of nitrogen isotopes in air trapped within the ice instead of isotopes in the ice itself, which had been used in past studies.

Not only did the new analysis detect significant warming in response to increasing atmospheric CO2, it documents a warming trend at a rate closely matching what climate change models predict should have happened as Earth shifted out of its ice age, according to lead author Christo Buizert, a postdoctoral researcher at Oregon State University and lead author on the Science article.

“The Greenland isotope records from the ice itself suggest that temperatures 12,000 years ago during the so-called Younger Dryas period near the end of the ice age were virtually the same in Greenland as they were 18,000 years ago when much of the northern hemisphere was still covered in ice,” Buizert said. “That never made much sense because between 18,000 and 12,000 years ago atmospheric CO2 levels rose quite a bit.”

“But when you reconstruct the temperature history using nitrogen isotope ratios as a proxy for temperature, you get a much different picture,” Buizert pointed out. “The nitrogen-based temperature record shows that by 12,000 years ago, Greenland temperatures had already warmed by about five degrees (Celsius), very close to what climate models predict should have happened, given the conditions.”

Reconstructing temperatures by using water isotopes provides useful information about when temperatures shift but can be difficult to calibrate because of changes in the water cycle, according to Edward Brook, an Oregon State paleoclimatologist and co-author on the Science study.

“The water isotopes are delivered in Greenland through snowfall and during an ice age, snowfall patterns change,” Brook noted. “It may be that the presence of the giant ice sheet made snow more likely to fall in the summer instead of winter, which can account for the warmer-than-expected temperatures because the snow records the temperature at the time it fell.”

In addition to the gradual warming of five degrees (C) over a 6,000-year period beginning 18,000 years ago the study investigated two periods of abrupt warming and one period of abrupt cooling documented in the new ice cores. The researchers say their leading hypothesis is that all three episodes are tied to changes in the Atlantic meridional overturning circulation (AMOC), which brings warm water from the tropics into the high northern latitudes.

The first episode caused a jump in Greenland’s air temperatures of 10-15 degrees (C) in just a few decades beginning about 14,700 years ago. An apparent shutdown of the AMOC about 12,800 years ago caused an abrupt cooling of some 5-9 degrees (C), also over a matter of decades.

When the AMOC was reinvigorated again about 11,600 years ago, it caused a jump in temperatures of 8-, 11 degrees (C), which heralded the end of the ice age and the beginning of the climatically warm and stable Holocene period, which allowed human civilization to develop.

“For these extremely abrupt transitions, our data show a clear fingerprint of AMOC variations, which had not yet been established in the ice core studies,” noted Buizert, who is in OSU’s College of Earth, Ocean, and Atmospheric Sciences. “Other evidence for AMOC changes exists in the marine sediment record and our work confirms those findings.”

In their study, the scientists examined three ice cores from Greenland and looked at the gases trapped inside the ice for changes in the isotopic ration of nitrogen, which is very sensitive to temperature change. They found that temperatures in northwest Greenland did not change nearly as much as those in southeastern Greenland — closest to the North Atlantic — clearly suggesting the influence of the AMOC.

“The last deglaciation is a natural example of global warming and climate change,” Buizert said. “It is very important to study this period because it can help us better understand the climate system and how sensitive the surface temperature is to atmospheric CO2.”

“The warming that we observed in Greenland at the end of the ice age had already been predicted correctly by climate models several years ago,” Buizert added. “This gives us more confidence that these models also predict future temperatures correctly.”

 

From Science

Greenland deglaciation puzzles

Louise Claire Sime, British Antarctic Survey, High Cross, Cambridge, CB23 7PP, UK.

About 23,000 years ago, the southern margins of the great Northern Hemisphere ice sheets across Europe and North America began to melt. The melt rate accelerated ∼20,000 years ago, and global sea level eventually rose by ∼130 m as meltwater flowed into the oceans. Ice cores from the Greenland and Antarctic ice sheets show the rise in atmospheric CO2 concentrations that accompanied this shift in global ice volume and climate. However, discrepancies in the temperature reconstructions from these cores have raised questions about the long-term relationship between atmospheric CO2 concentrations and Arctic temperature. On page 1177 of this issue, Buizert et al. (1) report temperature reconstructions from three locations on the Greenland ice sheet that directly address these problems.

Abstract

Greenland ice core water isotopic composition (δ18O) provides detailed evidence for abrupt climate changes but is by itself insufficient for quantitative reconstruction of past temperatures and their spatial patterns. We investigate Greenland temperature evolution during the last deglaciation using independent reconstructions from three ice cores and simulations with a coupled ocean-atmosphere climate model. Contrary to the traditional δ18O interpretation, the Younger Dryas period was 4.5° ± 2°C warmer than the Oldest Dryas, due to increased carbon dioxide forcing and summer insolation. The magnitude of abrupt temperature changes is larger in central Greenland (9° to 14°C) than in the northwest (5° to 9°C), fingerprinting a North Atlantic origin. Simulated changes in temperature seasonality closely track changes in the Atlantic overturning strength and support the hypothesis that abrupt climate change is mostly a winter phenomenon.

 

Original Science Daily article here

Science paper here

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It’s All About Fresh Water — Rapid Sea Level Rise Points To Massive Glacial Melt in Antarctica

Originally posted on robertscribbler:

It’s all about fresh water. In this case, massive freshwater outflows from the vast glaciers covering Antarctica.

This week, a new scientific report published in the Journal Nature found that from 1992 through 2012 freshwater outflow from Antarctica’s massive glaciers exceeded 400 gigatons each year. An immense flood of cold, fresh water. One that helped push sea levels rapidly higher around the Antarctic continent.

But with glacial melt on the rise and with mountains of ice now inexorably sliding seaward, these freshwater flows may just be the start of even more powerful outbursts to come. And such prospective future events have far-ranging implications for sea level rise, global weather, sea ice, human-caused climate change, and world ocean health.

Flood of Fresh Water Drives More Sea Level Rise Than Expected

The researchers discovered the tell-tale signature of this vast freshwater flood through chemical analysis of the seas surrounding Antarctica. The…

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A Time to Kill: Meryl Dorey and her AVsN give medical advice on seizures.

Originally posted on reasonablehank:

After an extensive investigation into the Australian Vaccination skeptics Network, the NSW Health Care Complaints Commission issued a Public Health Warning on April 30 2014 [my bold]:

Public warning

The Commission has established that AVN does not provide reliable informationin relation to certain vaccines and vaccination more generally. The Commission considers that AVN’s dissemination of misleading, misrepresented and incorrect information about vaccination engenders fear and alarm and is likely to detrimentally affect the clinical management or care of its readers.

Given the issues identified with the information disseminated by AVN, the Commission urges general caution is exercised when using AVN’s website or Facebook page to research vaccination and to consult other reliable sources, including speaking to a medical practitioner, to make an informed decision.

The Commission has recommended that AVN amend its published information with regard to the above issues and the Commission will monitor the implementation of these…

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Russia’s warming faster than the rest of the planet—and seeing disease, drought, and forest fires as a result

Originally posted on Quartz:

When Vladimir Putin declined to support the Kyoto Protocol, a treaty to limit carbon emissions, he famously quipped that higher temperatures might actually benefit Russia since its people would have to spend less on fur coats.

Well, he’s getting his wish. Changes in wind and ocean currents caused by global warming shift heat around unevenly, causing some areas to heat up dramatically even as other regions cool. Russia, it turns out, is in the unusually hot category. Between 1976 and 2012, average Russian temperatures rose 0.43°C (0.8°F) a decade—more than twice the global average of 0.17°C—according to a new report out by Russia’s climate and environment agency (pdf, link in Russian).

The increase in the average temperature in Russia.

Trends in Russia’s average temperatures.

This is a big problem for a variety of reasons, say Russia’s climate scientists. Hotter temperatures appear to be driving a spike in episodes of dangerous extreme weather:

Dangerous-extreme-weather-is-on-the-rise-in-Russia-Incidents-e-g-floods-drought-cyclones-5-year-moving-average_chartbuilder (2)

The frequency of forest fires

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Ice sheets thick as a denialist’s head

Originally posted on Millard Fillmore's Bathtub:

Cartoonist Randall Munroe at XKCD demonstrates ice age issues.

Of course it was a cartoonist. Where else does one go to find the truth these days, but the cartoons?

XKCD dramatically shows differences in North American cities and their relationship with their local ice sheets, 21,000 years ago.

XKCD dramatically shows differences in North American cities and their relationship with their local ice sheets, 21,000 years ago. Cartoon by Randall Munroe.

Enric Sala wrote about our disappearing ice for the World Economic Forum — a post worth reading.

Twenty kilometres in 20 years. That’s how much the Ilulissat glacier has retreated as this mighty, flowing river of ice crumbles into the ocean. It sounds like a lot. But I did not fully realize what this meant until we flew over the Ilulissat icefjord. It takes 10 minutes for the helicopter to fly over the amount of ice that has been lost because of global warming – in this glacier alone.

The speed at which the glacier moves has doubled…

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Information Aversion

Originally posted on Azimuth:

Why do ostriches stick their heads under the sand when they’re scared?

They don’t. So why do people say they do? A Roman named Pliny the Elder might be partially to blame. He wrote that ostriches “imagine, when they have thrust their head and neck into a bush, that the whole of their body is concealed.”

That would be silly—birds aren’t that dumb. But people will actually pay to avoid learning unpleasant facts. It seems irrational to avoid information that could be useful. But people do it. It’s called information aversion.

Here’s a new experiment on information aversion:

In order to gauge how information aversion affects health care, one group of researchers decided to look at how college students react to being tested for a sexually transmitted disease.

That’s a subject a lot of students worry about, according to Josh Tasoff, an economist at Claremont Graduate University who…

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Hunt launches personal attack on head of Australian solar lobby

Is this any way for a government minister to behave? The fact is, Greg Hunt is a AGW denier like the rest of his lunatic fringe party. He says he accepts the science underpinning climate change but then flags and implements policies that don’t reflect the science. He is either a fraud, completely incompetent or stupid…..or all three.

Hunt launches personal attack on head of Australian solar lobby.

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