Archive for the ‘Cryosphere’ Category

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Good Arctic sea ice pic and vid

28 September 2012

I’ve already blogged about the record Arctic sea ice melt. The following picture and video further illustrate the point. This graphic from the Australian Conservation Foundation shows what the Arctic melt would look like if Australia was melting:

Note that Arctic sea ice volume has declined even more dramatically, with four-fifths disappearing in the 34-year record.

This video from The Yale Forum on Climate Change & The Media also explains it well:

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Arctic sea ice minimum: A planetary emergency

21 September 2012

The news that Arctic sea ice is in meltdown is being treated as merely one news item among many, even though it threatens to set off a chain of tipping points affecting all of humanity and life on Earth. I’m reminded of how the iceberg warnings sent to the Titanic by other ships were interspersed with passenger messages, and the final and most urgent warning was not considered important enough to deliver to the captain. In 1912 it was the presence of Arctic ice that failed to sink in; in 2012 it is the absence thereof; but the lack of needed attention is the same.

After a spectacular melt season, the Arctic sea ice finally appears to have reached its annual minimum on 16 September. In a horrible milestone, the ice extent shrank to just 3.4 million square km, which is three-quarters of a million square km (or 18%) below the 2007 record low broken in late August, and less than half of the 1980s average. (Note that sea ice extent includes areas with only partial ice cover; actual sea ice area got as low as 2.2 million square km.)

Source: International Arctic Research Center

The ice has retreated so far as to make the Arctic Ocean circumnavigable:

Source: National Snow & Ice Data Center (NSIDC) Read the rest of this entry ?

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Arctic sea ice in a death spiral

29 August 2012

Source: International Arctic Research Center

As Australian politicians fiddle with the details of an extremely insufficient climate change policy, I’ve been watching Arctic sea ice news with increasing dismay. Summer sea ice in the Arctic is fast melting away, accelerated by amplifying feedbacks in what has been called a “death spiral”. The disappearance of Arctic summer sea ice is a key tipping point.

Sea ice floats on the ocean surface and is not to be confused with ice sheets on land. Arctic sea ice grows and shrinks seasonally, with an annual minimum in September. This year, eight independent datasets show we’ve already reached record low sea ice cover in the last week or so, with still weeks to go before the annual minimum.

In the IJIS Arctic sea ice extent dataset (pictured above), the previous record was 4.3 million square km on 24 September 2007 (with the 2011 minimum not far behind). This year we’re only up to 29 August, yet extent has already plummeted to 3.9 million square km. As if that’s not astonishing enough, the ice continues to shrink by 100,000 square km per day. Normally at this time of year, melting slows down as the melt season draws to a close – but this time it seems to be still accelerating, which is unprecedented in decades of observations. Nobody can predict what will happen next. Read the rest of this entry ?

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Is Greenland close to a climate tipping point?

25 July 2012

Recent findings suggest climate change in Greenland may be approaching a tipping point, beyond which amplifying feedbacks could lead (probably over centuries) to complete melting of the ice sheet, raising sea level by about 7 meters.

In June, a team of glaciologists led by Jason Box predicted that we would see melting across 100% of the ice sheet’s surface area in summer within a decade. They drew that conclusion from data on the Greenland ice sheet’s surface reflectivity, or “albedo”, showing the surface has gotten darker over the last 12 years. A darker surface absorbs more heat, leading to more melting, causing albedo to decrease further, and so on in a vicious circle.

The ice naturally gets less reflective in summer because the shape of the snowflakes changes, but in 2012 Greenland has become much darker than in previous summers. This is occurring particularly at high elevations, which were previously too cold to melt and indeed had gained ice from increasing snowfall. This month, at the height of the melt season, Greenland’s albedo has fallen far off the charts:


Figure 1: Surface albedo of the Greenland ice sheet (average of all elevations) between March and October in each year from 2000 to 2012. (Source: Ohio State University) Read the rest of this entry ?

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Christy Crock: Do the observations match the models?

21 April 2011

I wrote this post for Skeptical Science.

At the recent US House of Representatives Committee on Science Space and Technology climate hearing, the Republicans called Dr. John Christy as an expert witness testifying against the global warming consensus. Unfortunately, Christy spent his time repeating a long list of climate myths, including the common contrarian refrain that “climate model output does not match up to the real world”. Let’s examine this claim.

A tale of three climate indicators

Surface temperature observations are well within the range of model projections:

Observed global temperatures since 1980 compared to IPCC AR4 model projections Read the rest of this entry ?

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Climate Emergency: Time to Slam on the Brakes

8 March 2011

I wrote this post for Skeptical Science as a basic rebuttal of the argument “It’s not urgent”.

Global warming is an increasingly urgent problem. The urgency isn’t obvious because a large amount of warming is being delayed. But some of the latest research says if we want to keep the Earth’s climate within the range humans have experienced, we must leave nearly all the remaining fossil fuels in the ground. If we do not act now we could push the climate beyond tipping points, where the situation spirals out of our control. How do we know this? And what should we do about it? Read on.

James Hansen, NASA’s top climatologist and one of the first to warn greenhouse warming had been detected, set out to define dangerous human interference with climate. In 2008, his team came to the startling conclusion that the current level of atmospheric carbon dioxide (CO2) is already in the danger zone.

Since the Industrial Revolution, atmospheric CO2 has increased from 280 to 390 parts per million (ppm). Don’t be fooled by the small number – 390 ppm is higher than CO2 has been in millions of years. CO2 is rising by 2 ppm per year as we continue to burn fossil fuels. To stabilise the Earth’s climate, we must reduce CO2 to the relatively safe level of 350 ppm. And we must hurry, because the task will soon be an impossible one.

The 350 target is based not on climate modeling, but on past climate change (“paleoclimate”). Hansen looked at the highly accurate ice core record of the last few hundred thousand years, sediment core data going back 65 million years, and the changes currently unfolding. He discovered that, in the long term, climate is twice as sensitive in the real world as it is in the models used by the IPCC. Read the rest of this entry ?

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A basic overview of melting ice around the globe

17 February 2011

I wrote this post for Skeptical Science as a basic rebuttal of the argument “Ice isn’t melting”.

Contrary to contrarian claims, ice is melting at accelerating rates in the Arctic, Antarctica, Greenland, and glaciers all over the world. Arctic sea ice has shrunk by an area equal to Western Australia, and could be all gone in a decade.

Ice sheets are beginning to shrink

An ice sheet is a huge layer of land ice. The only ice sheets are in Antarctica and Greenland.

The Greenland ice sheet is losing mass at an accelerating rate. In recent years the ice loss has spread from the south coast around to the northwest.

Read the rest of this entry ?