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CLIMATE SCIENCE
UN report to point to mounting climate challenge
by Staff Writers
Paris (AFP) Sept 21, 2013


Climate: Growing certainties on warming and human role
Paris (AFP) Sept 21, 2013 - Over the past 23 years, UN scientists have issued progressively stronger assertions about climate change.

They have moved from a sketchy warning that heat-trapping carbon gases emitted by fossil fuels will cause a "greenhouse" effect to the conviction that this effect is now having an impact on Earth's climate.

Following are extracts from the Intergovernment Panel on Climate Change's assessment reports, the latest of which will be published from Friday.

First Assessment Report (1990)

"... emissions resulting from human activities are substantially increasing atmospheric concentrations of greenhouse gases...

"These increases will enhance the greenhouse effect, resulting on average in an additional warming of the Earth's surface."

Second Assessment Report (1995)

"Most of these studies have detected a significant change and show that the observed warming trend is unlikely to be entirely natural in origin...

"... the balance of evidence suggests that there is a discernible human influence on global climate.

"... the average rate of warming [in projections for the 21st century] would probably be greater than any seen in the last 10,000 years, but the actual annual to decadal changes would include considerable natural variability."

Third Assessment Report (2001)

"There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities.

"... the projected rate of warming is much larger than the observed changes during the 20th century and is very likely to be without precedent during at least the last 10,000 years, based on paleoclimate data."

The report said the global average temperature had risen by 0.6 degrees Celsius (1.08 degrees Fahrenheit) between 1901 and 2000.

Human activity was "likely" to be the cause of warming, a term meaning a probability of more than 66 percent.

Fourth Assessment Report (2007)

"Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level.

"Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic [man-made] greenhouse gas concentrations."

The report said that warming over the previous 100 years was 0.74 C (1.33 F), and 11 of the previous 12 years had been the warmest on record.

Human activity was "very likely" the cause of warming, meaning a probability of more than 90 percent.

Fifth Assessment Report (draft version seen by AFP)

"In the northern hemisphere, the period 1983-2012 was very likely the warmest 30-year period of the last 800 years and likely the warmest period of the last 1,400 years.

"....Greenhouse gases contributed a global mean surface warming likely to be in the range of 0.5-1.3 C [0.9-2.3 F] over the period 1951-2010."

"...There is high confidence that this has warmed the ocean, melted snow and ice, raised global mean sea level and changed some climate extremes in the second half of the 20th century."

Human activity was "extremely likely" to be the cause of this warming, meaning between 95 and 100 percent probability.

The draft attributes an observed slowing in warming from 1998 to 2012 -- a phenomenon cited by skeptics as evidence that warming is not man-made -- to a temporary cooling cycle in the weather system and lower-than-expected solar activity.

Temperatures since 1901 have risen by 0.89 C (1.6 F), it says.

Additional warming this century is estimated to range from 1.0 to 3.7 C (1.8-6.6 F), and sea level rise from 40 to 62 centimetres (16-24.8 inches), according to four projections based on how much carbon is emitted.

Scientists will hike pressure next week on the UN's troubled climate talks as they release a report pointing to the dizzying challenge of meeting the international body's target for global warming.

In the first volume of a massive trilogy, the Nobel-winning Intergovernmental Panel on Climate Change (IPCC) will publish its projections for warming by 2100.

Just a single scenario -- and by far the toughest to achieve -- sees the possibility of safely anchoring the temperature rise to within two degrees Celsius (3.6 degrees Fahrenheit), according to a draft seen by AFP.

In the other projections, the UN's much-trumpeted 2 C goal will be overshot.

At the very top of the range, warming would be more than double the UN target and more than triple that set by vulnerable small-island states.

Warming on this scale would gravely accentuate the peril from drought, flood, storms and rising seas.

"It's been known for a long time that we are running out of time," said Alden Meyer, with the US environmental group the Union of Concerned Scientists (UCS).

"The longer you wait, the more difficult it becomes and the more expensive it gets."

The UN's panel of climate scientists has issued only four overviews in 25 years. The last was in 2007 and despite fierce opposition from skeptics, climate science has made many advances since then.

The work released in Stockholm on Friday comprises a 2,000-page report authored by 257 scientists, plus a 31-page Summary for Policymakers.

Over the four preceding days, the summary will be vetted line by line by government representatives from 195 countries. Governments have a seat on the panel but are not allowed to censor the scientists' main report.

The draft document strengthens the IPCC's conviction in 2007 -- from 90 to 95 percent -- that humans are to blame for climate change.

It also sees four projections based on "radiative forcing," or the heat delivered to Earth's surface as a result of fossil-fuel gases and other carbon emissions that trap solar heat.

The lowest scenario sees an average temperature rise of 1.0 C (1.8 F) by 2100, ranging from 0.3 to 1.7 C (0.5-3.1 F).

The highest scenario has an average of 3.7 C (6.7 F), ranging from 2.6 C (4.7 F) to a whopping 4.8 C (8.6 F).

But around 0.8 C (1.4 F) must be added to all these figures to factor in warming since the start of the Industrial Revolution -- the yardstick used in the UN target.

Previous research into the lowest scenario says global carbon dioxide (CO2) emissions, currently scaling new highs, must peak by around 2020 and then decline sharply.

By the end of the century, emissions would even have to be negative compared with 2000, say some models.

In other words, some CO2 would have to be stripped out of the atmosphere to help the cooling -- something that has no precedent in recent human history.

True to tradition, the IPCC is mute on recommendations and what could be considered a safe maximum, although it cautions that reaching 2C will require "substantially lower" emissions.

Small island states that fear being drowned by rising seas are clamouring for an even more stringent target, of 1.5 C (2.7 F).

Climate's rise and fall as political issue

The IPCC co-won the Nobel Peace Prize after publishing its landmark Fourth Assessment Report, or AR4, in 2007.

After that, climate change as an issue went into decline after the near-fiasco of the 2009 Copenhagen Summit. And the IPCC's own reputation was dented by several mistakes that emerged in AR4.

Together, this enabled climate skeptics to assault the point of curbing greenhouse gases, especially as the world financial crisis began to grip rich economies.

Environmentalists, though, say climate change is a fact that cannot be ducked, and the IPCC is essential for addressing it as its work carries the imprimatur of governments.

"The IPCC is the foundation stone on which the whole of the climate movement is built and on which the whole of climate policy is founded," said Tim Nuthall of the European Climate Foundation.

"It will become the new playbook, just as AR4 did over time... if you take a step back, the report over the next few years will permeate down to so many sections of the economy and society."

Dealing with the greenhouse effect is a political nightmare, touching on high costs and powerful interests.

It entails weaning today's economies off their dependence on coal, oil and gas, the bedrock of their energy supply.

Efforts for a UN pact stumbled in Copenhagen in 2009. The next deadline is for 2015 -- and even this is beginning to look shaky.

"Greenhouse gases are altering Earth's climate. No serious politician on the planet can now dispute that," the science journal Nature said in an editorial on Wednesday.

But it added: "The governments of the world, to whom the IPCC reports, have made precious little headway in reducing emissions. And they appear in little hurry to do so."

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UN climate report will not sway US deniers: experts
Washington (AFP) Sept 21, 2013
The upcoming UN report on climate change is not likely to rattle US deniers of global warming who hold sway in the halls of power, experts say. A hefty analysis of the latest science on global climate change, the report is packed with recommendations for policymakers. It will be released at the Intergovernmental Panel on Climate Change (IPCC) next week, though most Republicans in the US ... read more


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