NASA’s James Hansen on the IPCC forecast


He is also one of the most outspoken of mainstream climate scientists, regularly and publicly clashing with his political masters in recent years.

But in his April testimony to the US Congress Hansen this time criticised the Intergovernmental Panel on Climate Change (IPCC) . Its newly published advice on predicted rises in sea levels, Hansen argued, was far from adequate.

If the NASA scientist’s calculations are correct, we face a problem far more serious than previously suggested. Hansen is convinced that if we continue to burn fossil fuels relentlessly there is no question coastal nations worldwide will experience unprecedented flooding.

Ice-cap row

Hansen’s dispute with the IPCC centres on what he suggests is an overly cautious approach to factoring in the speed at which the ice caps are melting.

In the IPCC’s 2001 report it predicted a sea level rise of about 0.7 metres from all causes by 2100. But the new IPCC report excludes melting ice sheets so gives lower estimates.

” Greenland and west Antarctica are home to the most vulnerable ice-sheets. If either sheet melted entirely it would raise sea levels by seven to eight metres.”

Hansen has himself taken a brave stab at estimating this most important and very uncertain component, suggesting that under typical “business as usual” scenarios the more likely figure by 2100 is several metres.

There is little argument over the volumes of ice and water involved. Scientists are confident they have fairly accurately calculated the amount of water now locked up in the great ice-caps of Greenland and Antarctica.

Greenland and west Antarctica are home to the most vulnerable ice-sheets. If either sheet melted entirely it would raise sea levels by seven to eight metres.

According to the IPCC, a global temperature increase of more than about 2°C would see Greenland’s ice-sheet eventually melt completely. And its projections show this degree of temperature change is now very likely by the end of the century.

But while there is no doubt about the final outcome, the uncertainty for the IPCC is over how fast Greenland’s ice-sheet will melt. The rates of all the melting processes are still very uncertain, nor are they properly represented by conventional models for predicting melting rates (see Extras: the science below).

” With the scientific community divided, such an uncertain forecast will leave policy makers struggling to plan ahead.”

Given this uncertainty, the IPCC in its report declined to make any quantitative estimates of sea level rises that might result, even within wide error bounds. What it did give was estimates of the smaller but much better understood effects of thermal expansion as the oceans warm, ranging from 0.2 to 0.6m by 2100.

This, Hansen thinks, was a serious error. He argues there is a major risk that sea levels will rise by several metres this century so a cursory look at the IPPC’s safe prediction of less than 1m gives an altogether false sense of security.

Faced with a major controversy, and real and serious uncertainty, the official watchdog has failed to bark, and Hansen is trying to fill the vacuum it has left. With the scientific community divided, such an uncertain forecast will leave policy makers struggling to plan ahead.

Stern warning

Previous considerations of risks associated with rising sea levels, including the Stern Report, have tended to stick with the conventional “maybe a metre per century”.

Nevertheless all agree it is a serious problem that will either cause massive damage or incur massive costs in adaptations needed to prevent damage – or both.

The rise in sea levels since 1900 has been modest at about 0.2m, mainly due to the relatively small effects of thermal expansion and melting mountain glaciers. But the now rapid melting of large ice-sheets is causing increased concern.

A separate issue for areas a few metres above sea level is flooding caused by heavy rainfall, but in low lying areas such as Bangladesh this combined with rising sea levels is making the overall effect much worse.

There is serious doubt that we can afford to protect the world’s major coastal cities – London, New York, Mumbai and Shanghai – against sea-level rise of several metres.

According to Hansen, large areas of Florida, East Anglia and the Netherlands, as well as many oceanic islands and most of Bangladesh, could be inundated within the lifetime of children now being born.

Speaking exclusively to, Hansen said: “Energy departments the world round don’t get it yet. We should not be building any new coal-fired power plants that do not capture and store the CO2.”

If we are to retain any hope of keeping sea levels relatively steady, he argues, those power plants will need to be bulldozed over the next few decades.

Damage limitation

If there is a real risk that this problem may now be several times worse than previously thought, it strengthens the case made by Stern that mitigation – reducing CO2 and other greenhouse gas emissions – represents an excellent investment, even if the cost of doing so is far from trivial.

In Hansen’s view, allowing the atmospheric CO2 level to rise even to 450 parts per million (ppm), corresponding to a global warming of about 2°C, may be to go too far.

Atmospheric CO2 is currently about 380ppm, already far above the pre-industrial level of 280ppm, and rising at almost 2ppm per year.

This gives us at most just a few decades to take drastic action. Within 50 years, but preferably sooner, we would have to cut global CO2 emissions by, at the least, a factor of four; in plain terms, by 75%.

The targets set under the Kyoto protocol are just a very small step in the right direction. The UK target for a 60% cut by 2050 seems broadly consistent with what is needed. But it overlooks a rapid rise in emissions elsewhere, and especially in China, which means the developed world will have to make even deeper cuts.

Ethical arguments support the adoption of a “contraction and convergence” policy. This would see total global emissions progressively reduced, with per capita emissions in different countries gradually equalised over time to less than 0.4 tonnes for every person.

In this scenario, Europe could expect to have to aim for a 90% cut by 2100, and the USA for a 95% cut over the same time. Even China and India will have to halt their rising emissions, eventually reducing them albeit by smaller amounts to achieve stabilisation. To say the least, these are seriously challenging goals.

Is this de-carbonisation of the global economy achievable? No one can foresee the technology of 100 or even 50 years into the future so the short answer is: we don’t know. But businesses can make a start.

Economic incentive

In a now world-wide market economy, putting a serious price on carbon emissions would provide a clear and significant incentive for the development and use of all types of renewable and low-carbon energy sources.

It would also encourage methods for capturing and storing CO2 generated by continued use of fossil fuels, while they last.

This could be done by levelling a carbon tax or, less directly, through cap and trade schemes such as the European emissions trading scheme.

But as teething troubles with the emissions trading scheme have shown, these schemes rely heavily on getting the level of emissions limits right. Most businesses would probably prefer stable and predictable prices for carbon emissions, which a carbon tax can provide. Traders who profit from market fluctuations might have other ideas.

There is however no doubt that a new form of indirect taxation through a carbon tax would prove unpopular and regressive. So it would make sense to make it a revenue-neutral replacement for another existing unpopular and regressive indirect tax, such as sales taxes or, in Europe, VAT.

Recent statements by Britain’s new prime minister, Gordon Brown, suggest that within Europe this may no longer be an impossible goal.

For more intractable sectors of the economy, direct regulation of emissions may be needed. This would apply notably to transport and especially aviation, which currently has no alternative to fossil fuels.

And while hydrogen may be the fuel of the future, regrettably its generation is now largely done through use of fossil fuels. If hydrogen is to play a role in solving transport problems, we desperately need a low carbon (solar or possibly nuclear) way to produce it, along with better and lighter ways to store it.

Business imperative

We need to make the shift from a position where global emissions are increasing at about 2% per year to one where they decrease at about 2% per year, and within a few decades at most.

The change will require major economic incentives and a much more effective global emissions limitation scheme. Even if we develop the right clean technologies, the financial incentives will be needed to help implement them.

For businesses this means planning ahead for a future where energy costs will be much higher, especially where derived from fossil fuels. This is the inevitable, and intended, consequence of both any carbon-trading scheme, and a carbon tax.

Businesses and the financial community are already thinking hard how to turn this threat into an opportunity. PriceWaterhouseCoopers notably looked into the effect of carbon regulations on businesses in its recent report “Saving the planet: can tax and regulation help?”.

We also need to look with grave misgiving at all existing infrastructure and new investments located within a few metres of sea level.

And above all, we need to be ready for change, for surprises, and for more extreme events. It’s likely to be a bumpy ride.

Extras: the science

Until recently, the growth and decline of ice-sheets was believed to be a very slow process, stretching over thousands of years. An ice-sheet can only grow as fast as snow accumulates, generally at less than 1m per year when it is compacted into ice, so an ice-sheet several thousand metres thick must take thousands of years to build up.

Ice-sheets then get smaller and lose mass, mainly in two ways. The first is melting, at both the surface and the base when the temperature is greater than 0°C. The base is often relatively warmer than the surface, because of geothermal heating from the interior of the Earth.

Secondly, the sheets lose mass by disintegrating at the edges, calving icebergs into the sea, often after the ice has first flowed offshore to create massive floating ice-shelves.
Ice lost this way is replaced by more ice flowing from the interior, via glaciers and ice-streams. In the past, glaciologists have generally considered this a slow process.

Their computer models have reflected this view so the whole process of melting and calving, and the resulting rise in sea level, has been predicted to take thousands rather than hundreds of years.

However, the last few years have brought some surprises. First, we have seen that floating ice-shelves can disintegrate quite suddenly, over just a few weeks. The collapse of the Larsen B ice-shelf off the Antarctic peninsula in 2002 is a classic example.

Another big surprise was the subsequent discovery that ice-streams – the “rivers” of ice that flow relatively fast within glaciers – that fed the ice-shelf had accelerated dramatically after the shelf disappeared.

The buttressing effect of the ice-shelf, holding back the glaciers and ice streams, seems too be much greater than glaciologists had thought.

The third surprise was recent measurements of both gravity and surface elevation from satellites showing that both Greenland and west Antarctica are losing mass much faster than expected.

In both cases it seems “warm” ice, near its melting point, is responsible. This ice is relatively wet, and melt-water is known to create a slurry that lubricates the flow of glaciers over the rock beneath, allowing them to flow much faster.

And it now seems water also percolates into “warm” ice much more than was expected, sometimes flowing right through glaciers in “moulins” to lubricate their beds, and even through ice-shelves, causing them to fracture.

West Antarctica, it appears, is less prone to melt than Greenland’s ice-sheet. But, worryingly, it is grounded on land below sea level so it may also be vulnerable to melting by sea-water, from below.

The even larger east Antarctic ice-sheet is thought to be more secure but the big question is: how much melting will occur, and how fast?”

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