Archive for the ‘Skeptical Science’ Category

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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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Zero Carbon Australia: We can do it

3 April 2011

I wrote this post for Skeptical Science.

My recent post about long-term CO2 targets was rather doom-and-gloom: I concluded that we must phase out fossil fuels to keep the climate in the range that humans have experienced. The good news is that action on this scale is not only possible but surprisingly feasible.

Last year, the University of Melbourne Energy Research Institute in conjunction with Beyond Zero Emissions produced the Zero Carbon Australia 2020 Stationary Energy Plan. The ZCA2020 Plan outlines an ambitious and inspiring vision: to power Australia with 100% renewable energy in ten years.

The report that has been released only covers emissions from Stationary Energy (though it does refer to electrifying transport). Five future reports are planned on how to eliminate emissions from other sectors (Transport, Buildings, Land Use and Agriculture, Industrial Processes, and Replacing Fossil Fuel Export Revenue).

Why do it, and why now?

As I’ve explained here, to prevent “dangerous anthropogenic interference with the climate system” we must reduce CO2 to below 350 ppm. That necessitates a rapid transition to a zero-carbon economy.

A common approach is to define a quota of allowable future global emissions to limit warming to less than 2°C above predindustrial levels, and divide them up by nation per capita. At Australia’s current rate of emissions, we will use up our share of the global budget in just five years (the same goes for the US and Canada). This gives Australia about a decade to make the transition. 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 ?

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2010: A Year of Record Warmth and Weird Weather

24 January 2011

Last year’s global temperatures are in, and the result is that 2010 is statistically tied with 2005 for the title of the warmest year since records began in 1880.

According to the US National Oceanic and Atmospheric Administration’s National Climatic Data Center (NOAA NCDC), the global temperature for both years was 0.62°C above the 20th-century average 13.9°C; 2010 came second by a thousandth of a degree. (Climatologists usually give temperatures as anomalies relative to an average, because they are easier to compare than absolute temperatures. The last month with a temperature below average was February 1985.)

2010 set new records for the warmest March, April, May, and June. Indeed, when the seasonal cycle is removed March 2010 was the third warmest month of all time (April, May, and November 2010 were also among the top 20). The ten warmest years according to NCDC are 2005/2010, 1998, 2003/2002, 2006/2009, 2007, 2004, and 2001. The 15 warmest years have all occurred since 1995; every year since 1976 has been above average. The 2000s are the warmest decade on record, followed by the 1990s and 1980s.

2010 was the Northern Hemisphere’s warmest year and the Southern Hemisphere’s sixth warmest. The former had its warmest April, May, June, July, August, and November in 2010, while the latter had its warmest February. There was particularly strong warmth in Greenland, Canada, northern Africa, and the Middle East; as well as warmer than average temperatures in southern Africa, eastern Europe, eastern Russia, and southern Asia; and cooler than average temperatures in central Russia and northern Europe. Except for the eastern Pacific, most of the oceans were warmer than average; the North Atlantic was particularly warm.

Source: NOAA National Climatic Data Center

Read the rest of this entry ?

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Monckton Myth: Global Sea Ice

22 January 2011

I wrote this post for Skeptical Science as part of an ongoing series looking at the arguments made by Christopher Monckton against climate science.

This post examines Monckton’s arguments about global sea ice. Monckton claims:

[T]he global sea ice record shows virtually no change throughout the past 30 years, because the quite rapid loss of Arctic sea ice since the satellites were watching has been matched by a near-equally rapid gain of Antarctic sea ice.

Global Sea Ice Is Decreasing

Have Arctic ice losses truly been balanced by Antarctic gains? The first point to clarify is that we are talking about floating sea ice, not to be confused with land ice. Land ice at both poles and in glaciers around the world is sliding into the ocean at an accelerating rate. This net loss of land ice is contributing to sea level rise.

However, Monckton is clearly referring to sea ice. The rapid decline of Arctic sea ice has indeed coincided with an increase in Antarctic sea ice. But do these two opposite trends cancel out as Monckton suggests? In reality, the upward Antarctic trend is only slight compared to the plummeting Arctic trend. Tamino has crunched the numbers and found the Arctic trend is in fact more than three times faster than the Antarctic one. The net result is a statistically significant global decrease of more than a million km2 – would you agree with Monckton that this is “virtually no change”?

Figure 1: Global sea ice extent since 1979. (Image source: Tamino. Data is from US National Snow and Ice Data Center.) Read the rest of this entry ?