Tag Archives: Ice Age

Arctic is warmer than in 40,000 years

FOR IMMEDIATE RELEASE Average summer temperatures in the Canadian Arctic are now at the highest they’ve been for approaching 50,000 years, new evidence suggests. LONDON, 24 October – Good news for Arctic mosses, if not for any other Arctic creatures: little tundra plants that have been buried under the Canadian ice can feel the sunlight for the first time in at least 44,000 years. The implication is that the Arctic is now, and has been for the last 100 years, warmer than at any time in the last 44,000 years and perhaps for the last 120,000 years. This also means that the Arctic is warmer now than it was in what geologists call the early Holocene, the end of the last Ice Age – when the peak summer sunlight was roughly nine per cent greater than it is today, according to Gifford Miller of the University of Colorado Boulder, in the US. The mosses studied by Dr Miller, of course, could feel nothing: they were dead. But they could tell a story, all the same. The Arctic ice cap has been in constant retreat for the last century, and glaciers almost everywhere have been melting: there are fears that the process has begun to accelerate as greenhouse gases concentrate in the atmosphere. But as the ice recedes, it exposes evidence of the past, preserved over the millennia in the natural deep freeze.

Creating a timeline of climate change

The researchers used a technique called radiocarbon dating to establish that the mosses had been screened from the elements for at least 44,000 to 51,000 years. Since radiocarbon dating is only accurate for about 50,000 years, the mosses could have been buried for perhaps 120,000 years, since the last “interglacial” when the polar regions experienced a natural thaw. Miller and colleagues report in Geophysical Research Letters that they did their fieldwork on Baffin Island in the Arctic Circle, and measured the radiocarbon ages of the dead mosses in at least four different locations. They were careful to pick their 145 samples within one metre of the receding ice cap. Since the ice is receding at two or three metres a year, they could be sure the plant tissues had just been exposed that season. Since the plants could only have taken root in sunlight, they were evidence that the exposed terrain was once free of ice. They became silent witnesses, telling researchers about the changes through time in the frozen North. “The key piece here is just how unprecedented the warming of Arctic Canada is. This study really says the warming we are seeing is outside any kind of known natural variability, and it has to be due to increased greenhouse gases in the atmosphere,” said Miller.

Recent decades critical

Since radiocarbon clocks can only tick for so long, the Colorado team used ice cores to provide clues to the climate history of Baffin Island: each winter’s snowfall and summer melt is preserved in the icepack and like the growth rings in a tree provides a calendar of annual change. The last time temperatures on Baffin Island were as high as today was about 120,000 years ago. About 5,000 years ago, after a mellow period in the early Holocene, the Arctic began to cool again, and stayed cool until the beginning of the last century. “Although the Arctic has been warming since about 1900, the most significant warming in the region didn’t really start until the 1970s,” said Dr Miller. “And it really is in the last 20 years that the warming signal from that region has been just stunning. All of Baffin Island is melting, and we expect all of the ice caps to disappear, even if there is no additional warming.” – Climate News Network

FOR IMMEDIATE RELEASE Average summer temperatures in the Canadian Arctic are now at the highest they’ve been for approaching 50,000 years, new evidence suggests. LONDON, 24 October – Good news for Arctic mosses, if not for any other Arctic creatures: little tundra plants that have been buried under the Canadian ice can feel the sunlight for the first time in at least 44,000 years. The implication is that the Arctic is now, and has been for the last 100 years, warmer than at any time in the last 44,000 years and perhaps for the last 120,000 years. This also means that the Arctic is warmer now than it was in what geologists call the early Holocene, the end of the last Ice Age – when the peak summer sunlight was roughly nine per cent greater than it is today, according to Gifford Miller of the University of Colorado Boulder, in the US. The mosses studied by Dr Miller, of course, could feel nothing: they were dead. But they could tell a story, all the same. The Arctic ice cap has been in constant retreat for the last century, and glaciers almost everywhere have been melting: there are fears that the process has begun to accelerate as greenhouse gases concentrate in the atmosphere. But as the ice recedes, it exposes evidence of the past, preserved over the millennia in the natural deep freeze.

Creating a timeline of climate change

The researchers used a technique called radiocarbon dating to establish that the mosses had been screened from the elements for at least 44,000 to 51,000 years. Since radiocarbon dating is only accurate for about 50,000 years, the mosses could have been buried for perhaps 120,000 years, since the last “interglacial” when the polar regions experienced a natural thaw. Miller and colleagues report in Geophysical Research Letters that they did their fieldwork on Baffin Island in the Arctic Circle, and measured the radiocarbon ages of the dead mosses in at least four different locations. They were careful to pick their 145 samples within one metre of the receding ice cap. Since the ice is receding at two or three metres a year, they could be sure the plant tissues had just been exposed that season. Since the plants could only have taken root in sunlight, they were evidence that the exposed terrain was once free of ice. They became silent witnesses, telling researchers about the changes through time in the frozen North. “The key piece here is just how unprecedented the warming of Arctic Canada is. This study really says the warming we are seeing is outside any kind of known natural variability, and it has to be due to increased greenhouse gases in the atmosphere,” said Miller.

Recent decades critical

Since radiocarbon clocks can only tick for so long, the Colorado team used ice cores to provide clues to the climate history of Baffin Island: each winter’s snowfall and summer melt is preserved in the icepack and like the growth rings in a tree provides a calendar of annual change. The last time temperatures on Baffin Island were as high as today was about 120,000 years ago. About 5,000 years ago, after a mellow period in the early Holocene, the Arctic began to cool again, and stayed cool until the beginning of the last century. “Although the Arctic has been warming since about 1900, the most significant warming in the region didn’t really start until the 1970s,” said Dr Miller. “And it really is in the last 20 years that the warming signal from that region has been just stunning. All of Baffin Island is melting, and we expect all of the ice caps to disappear, even if there is no additional warming.” – Climate News Network

Why we should be cooling, not warming

EMBARGOED until 1900 GMT on Thursday 7 March Reconstructing the climate over the last 11,000 years shows that the Earth was once warmer than it is now – but that it would still be cooling today without the influence of greenhouse gases. LONDON, 7 March – US scientists have checked climate history for the past 11,300 years and come to one comforting conclusion. It has been warmer in human history, but those long hot summers happened long before the invention of cities, empires and scribes to record them. But soon all records will be broken: by 2100, when global temperatures will be higher than at any point since the end of the last Ice Age, according to a study in the journal Science (see EurekAlert! for the release). Shaun Marcott and colleagues from Oregon State University and Harvard University decided to look once again at the big picture. They examined reconstructions of past climates from fossil data, along with isotopes from terrestrial and marine sediments, from 73 sites around the globe, and tried to assess the main trends of climate change from the beginning of the Holocene – the geologists’ label for the epoch in which we now live. They chose to go as far back as possible in time across a wide range of locations, because there are always arguments about the reliability of readings from, say, tree rings, or indirect evidence from European monastic or naval records in the past 1500 years. These suggest an unprecedented warming, but the researchers felt that a clearer picture should emerge over a longer timespan.

Only one explanation

  “When you look at just one part of the world, the temperature history can be affected by regional climate variations. But when you combine the sites from all around the world, you can average out those regional anomalies and get a clear sense of the Earth’s global temperature history”, said Peter Clark, a co-author. They found that, for the first 5,000 years after the end of the Ice Age, the world warmed by about 0.6°C. Then from about 5,500 years before the present to just 100 years ago, there was a slow cooling of about 0.7°C, reaching a low point during the so-called Little Ice Age, when Londoners held “frost fairs” on the frozen Thames. This cooling, the researchers say, is linked to a 2°C temperature change in the North Atlantic. Such changes were almost certainly linked to cycles in the Earth’s orbit and to changes in the planet’s orientation that affect the levels of sunlight hitting the northern hemisphere. “As the Earth’s orientation changed, northern hemisphere summers became cooler, and we should almost be near the bottom of a long-term cooling trend – but obviously, we are not”, said Dr Marcott. The world should, in other words, still be in a cool phase. But in the last century, global temperatures have increased rapidly: from very nearly the coldest to the warmest levels of the Holocene. The only variable that can explain the rise is the rapid increase in carbon dioxide emissions due to human activity (see our story of 6 March, Coal triggers carbon level rise). And although the world is now warmer than it has been for most – but not all – of the last 11,300 years, by 2100, according to virtually every climate model, average global temperatures will be higher than at any time since the end of the Ice Age. – Climate News Network

EMBARGOED until 1900 GMT on Thursday 7 March Reconstructing the climate over the last 11,000 years shows that the Earth was once warmer than it is now – but that it would still be cooling today without the influence of greenhouse gases. LONDON, 7 March – US scientists have checked climate history for the past 11,300 years and come to one comforting conclusion. It has been warmer in human history, but those long hot summers happened long before the invention of cities, empires and scribes to record them. But soon all records will be broken: by 2100, when global temperatures will be higher than at any point since the end of the last Ice Age, according to a study in the journal Science (see EurekAlert! for the release). Shaun Marcott and colleagues from Oregon State University and Harvard University decided to look once again at the big picture. They examined reconstructions of past climates from fossil data, along with isotopes from terrestrial and marine sediments, from 73 sites around the globe, and tried to assess the main trends of climate change from the beginning of the Holocene – the geologists’ label for the epoch in which we now live. They chose to go as far back as possible in time across a wide range of locations, because there are always arguments about the reliability of readings from, say, tree rings, or indirect evidence from European monastic or naval records in the past 1500 years. These suggest an unprecedented warming, but the researchers felt that a clearer picture should emerge over a longer timespan.

Only one explanation

  “When you look at just one part of the world, the temperature history can be affected by regional climate variations. But when you combine the sites from all around the world, you can average out those regional anomalies and get a clear sense of the Earth’s global temperature history”, said Peter Clark, a co-author. They found that, for the first 5,000 years after the end of the Ice Age, the world warmed by about 0.6°C. Then from about 5,500 years before the present to just 100 years ago, there was a slow cooling of about 0.7°C, reaching a low point during the so-called Little Ice Age, when Londoners held “frost fairs” on the frozen Thames. This cooling, the researchers say, is linked to a 2°C temperature change in the North Atlantic. Such changes were almost certainly linked to cycles in the Earth’s orbit and to changes in the planet’s orientation that affect the levels of sunlight hitting the northern hemisphere. “As the Earth’s orientation changed, northern hemisphere summers became cooler, and we should almost be near the bottom of a long-term cooling trend – but obviously, we are not”, said Dr Marcott. The world should, in other words, still be in a cool phase. But in the last century, global temperatures have increased rapidly: from very nearly the coldest to the warmest levels of the Holocene. The only variable that can explain the rise is the rapid increase in carbon dioxide emissions due to human activity (see our story of 6 March, Coal triggers carbon level rise). And although the world is now warmer than it has been for most – but not all – of the last 11,300 years, by 2100, according to virtually every climate model, average global temperatures will be higher than at any time since the end of the Ice Age. – Climate News Network