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(The author is a Reuters market analyst. The views expressed are his own.)
By Gerard Wynn
LONDON, Jan 26 (Reuters) - If public interest in climate change can be measured by political speeches, the issue has fallen on hard times haunted by uncertainty in the science and a continuing economic downturn which demands attention.
In his 7,000-word, annual State of the Union address, U.S. President Barack Obama on Tuesday mentioned the words "climate change" once, while some Republican contenders for the November national election deny the problem exists.
In Europe only a handful of 27 European Union member states supports a shift to tougher climate targets.
Urgency to address climate science is hobbled by uncertainty in the underlying science, which has been exploited by sceptics in a sometimes brutal debate with activists which has added to the confusion.
Climate science deals almost exclusively in probabilities which are less likely to grab people burdened with financial worries and governments battling to shore up their economies.
Three years ago world leaders were mobilising to try and agree a global climate deal and Obama's administration was hoping to pass a climate bill.
Both initiatives flopped.
The sight of back-pedalling politicians suggests scientists must renew their strategy for understanding and communicating risk if interest isn't to ebb further.
What do we actually know for sure about climate change?
We only know that the world is getting warmer; carbon dioxide (CO2) levels in the atmosphere are rising; and that the CO2 build-up is the fault of humankind, as a result of emissions from burning fossil fuels and deforestation.
Such human emissions are "very likely" (U.N. language) to be contributing to a strong global average warming trend since the late 1970s at nearly 0.2 degrees Celsius per decade (after removing the effects of natural variation).
Scientists argue risk is greater on the upside: the lower bound of warming has barely changed at an expected further 2 degrees Celsius warming this century, but the upper bound has if anything risen with scientific understanding, and is more open at 4 degrees or more.
But there's the problem: it's impossible to forecast just how much warming there will be because of complex, so-called feedback effects.
For example, climate change may itself alter cloud formation in a way which adds yet more warming, or less, scientists aren't quite sure. And there are other feedback and non-linear effects ("tipping points") which are poorly understood.
Even bigger uncertainties lurk behind the impact of warming: the question of when and where climate change will become dangerous, and to whom.
Estimating global impacts such as sea level rise adds a tangled planetary response on top of the estimated warming.
Narrowing further to regional impacts, such as expected temperature and rainfall changes in a particular region or country, and the scientific mist thickens in the most pressing and least understood research area.
Until now governments seeking objective advice on future climate impacts turned to a report in 2007 by the U.N. Intergovernmental Panel on Climate Change (IPCC).
Famously, the review of impacts made a basic factual error, predicting the possible complete melt of all Himalayan glaciers by 2035, hundreds of years sooner than scientists' projections.
But more importantly its broader assessment of uncertainty around impacts was too vague.
To communicate risk better, governments and scientists must explicitly explain observed and future climate impacts for example from hazardous weather events (hurricanes, heatwaves and floods), where evidence has grown for a climate change fingerprint.
For example, in India it is "clearly seen" that there are fewer rain days and when it does rain it's heavier - risking flash flooding and damage to infrastructure and crop yields - say scientists at Britain's Metoffice Hadley Centre.
Britain on Thursday published its "UK Climate Change Risk Assessment", a good example of a focus on impacts.
But it's not enough just to make climate change real: the uncertainties need to be spelled out, if not resolved, and especially those elusive feedback effects which account for the wide range in estimated warming this century.
Meanwhile a resurgence in political interest will depend not only on a more coherent explanation of the science but timing.
Obama's reluctance to use words like "climate change" and "carbon emissions" also reflects a weakened position in Congress and a resurgence of conservative voters.
Re-election may embolden him to push the climate agenda once more, especially if impacts themselves intervene as arguably they did in a drought and heatwave in Texas last year. (Editing by Keiron Henderson)