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Why Hasn't Earth Warmed as Much as Expected?

Planet Earth has warmed much less than expected during the industrial era based on current best estimates of Earth's "climate sensitivity" - the amount of global temperature increase expected in response to a given rise in atmospheric concentrations of carbon dioxide (CO2). In a study to be published in the Journal of Climate, a publication of the American Meteorological Society (the early online release of the paper is available starting 19 January 2010; the link is given below), Stephen Schwartz, of Brookhaven National Laboratory, and colleagues examine the reasons for this discrepancy.
According to current best estimates of climate sensitivity, the amount of CO2 and other heat-trapping gases added to Earth's atmosphere since humanity began burning fossil fuels on a significant scale during the industrial period would be expected to result in a mean global temperature rise of 3.8°F - well more than the 1.4°F increase that has been observed for this time span. Schwartz's analysis attributes the reasons for this discrepancy to a possible mix of two major factors: 1) Earth's climate may be less sensitive to rising greenhouse gases than currently assumed and/or 2) reflection of sunlight by haze particles in the atmosphere may be offsetting some of the expected warming.

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Space agencies join forces to systematically observe climate variables

Over 30 000 people from 190 nations are gathered at the two-week UN Climate Change Conference in Copenhagen. On Thursday about 150 distinguished guests attended an ESA-hosted side event entitled 'Global Monitoring of our Climate: the Essential Climate Variables'.
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Temperature may hit high in 2010

The global average temperature could reach a record high in 2010, according to the UK's Met Office.
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2000-2009, The Warmest Decade

The year 2009 is likely to rank in the top 10 warmest on record since the beginning of instrumental climate records in 1850, according to data sources compiled by the World Meteorological Organisation (WMO).
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Sea levels are likely to rise by about 1.4m (4ft 6in) globally by 2100 as polar ice melts, according to a major review of climate change in Antarctica.
Conducted by the Scientific Committee on Antarctic Research (SCAR), it says that warming seas are accelerating melting in the west of the continent.
Ozone loss has cooled the region, it says, shielding it from global warming.

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This year 'in top five warmest'
This year will be one of the top five warmest years globally since records began 150 years ago, according to figures compiled by the Met Office.

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When most of us think about Ice Ages, we imagine a slow transition into a colder climate on long time scales. Indeed, studies of the past million years indicate a repeatable cycle of Earth's climate going from warm periods ("interglacial", as we are experiencing now) to glacial conditions.
The period of these shifts are related to changes in the tilt of Earth's rotational axis (41,000 years), changes in the orientation of Earth's elliptical orbit around the sun, called the "precession of the equinoxes" (23,000 years), and to changes in the shape (more round or less round) of the elliptical orbit (100,000 years). The theory that orbital shifts caused the waxing and waning of ice ages was first pointed out by James Croll in the 19th Century and developed more fully by Milutin Milankovitch in 1938.
undefined Ice age conditions generally occur when all of the above conspire to create a minimum of summer sunlight on the arctic regions of the earth, although the Ice Age cycle is global in nature and occurs in phase in both hemispheres. It profoundly affects distribution of ice over lands and ocean, atmospheric temperatures and circulation, and ocean temperatures and circulation at the surface and at great depth.
Since the end of the present interglacial and the slow march to the next Ice Age may be several millennia away, why should we care? In fact, won't the build-up of carbon dioxide (COČ) and other greenhouse gasses possibly ameliorate future changes?
Indeed, some groups advocate the benefits of global warming, including the Greening Earth Society and the Subtropical Russia Movement. Some in the latter group even advocate active intervention to accelerate the process, seeing this as an opportunity to turn much of cold, austere northern Russia into a subtropical paradise.
Evidence has mounted that global warming began in the last century and that humans may be in part responsible. Both the Intergovernmental Panel on Climate Change (IPCC) and the US National Academy of Sciences concur. Computer models are being used to predict climate change under different scenarios of greenhouse forcing and the Kyoto Protocol advocates active measures to reduce COČ emissions which contribute to warming.
Thinking is centred around slow changes to our climate and how they will affect humans and the habitability of our planet. Yet this thinking is flawed: It ignores the well-established fact that Earth's climate has changed rapidly in the past and could change rapidly in the future. The issue centers around the paradox that global warming could instigate a new Little Ice Age in the northern hemisphere.

Source Woods Hole Oceanographic Institution


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Greenland ice cap melting faster than ever
Satellite observations and a state-of-the art regional atmospheric model have independently confirmed that the Greenland ice sheet is loosing mass at an accelerating rate, reports a new study in Science.


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The possibility that climate change might simply be a natural variation like others that have occurred throughout geologic time is dimming, according to evidence in a Proceedings of the National Academy of Sciences paper published October 19.
The research reveals that sediments retrieved by University at Buffalo geologists from a remote Arctic lake are unlike those seen during previous warming episodes.
The UB researchers and their international colleagues were able to pinpoint that dramatic changes began occurring in unprecedented ways after the midpoint of the twentieth century.

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Title: Recent changes in a remote Arctic lake are unique within the past 200,000 years
Authors: Yarrow Axforda, Jason P. Brinerb, Colin A. Cookec, Donna R. Francisd, Neal Micheluttie, Gifford H. Millera,f, John P. Smole, Elizabeth K. Thomasb, Cheryl R. Wilsone and Alexander P. Wolfec

The Arctic is currently undergoing dramatic environmental transformations, but it remains largely unknown how these changes compare with long-term natural variability. Here we present a lake sediment sequence from the Canadian Arctic that records warm periods of the past 200,000 years, including the 20th century. This record provides a perspective on recent changes in the Arctic and predates by approximately 80,000 years the oldest stratigraphically intact ice core recovered from the Greenland Ice Sheet. The early Holocene and the warmest part of the Last Interglacial (Marine Isotope Stage or MIS 5e) were the only periods of the past 200,000 years with summer temperatures comparable to or exceeding today's at this site. Paleoecological and geochemical data indicate that the past three interglacial periods were characterized by similar trajectories in temperature, lake biology, and lakewater pH, all of which tracked orbitally-driven solar insolation. In recent decades, however, the study site has deviated from this recurring natural pattern and has entered an environmental regime that is unique within the past 200 millennia.

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Four degrees of warming 'likely'
In a dramatic acceleration of forecasts for global warming, UK scientists say the global average temperature could rise by 4C (7.2F) as early as 2060.
The Met Office study used projections of fossil fuel use that reflect the trend seen over the last 20 years.
Their computer models also factored in new findings on how carbon dioxide is absorbed by the oceans and forests.


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