Warnings: Global warming could lead to a catastrophe for humankind in 2100


Under a dual onslaught of global warming and localised, urban heating, some of the world's cities may be as much as eight degrees Celsius (14.4 degrees Fahrenheit) warmer by 2100, researchers warned on Monday. Such a temperature spike can have dire consequences for the health of city-dwellers, robbing companies and industries of able workers, and put pressure on already strained natural resources such as water.
The projection is based on the worst-case-scenario assumption that emissions of planet-warming greenhouse gases continue to rise throughout the 21st century. The top quarter of most populated cities, in this scenario, could see the mercury rise 7 C or more by century's end, said a study in the journal Nature Climate Change.
For some, nearly 5 degrees of the total would be attributed to average global warming. The rest would be due to the so-called Urban Heat Island (UHI) effect, which occurs when cooling parks, dams and lakes are replaced by heat-conducting concrete and asphalt — making cities warmer than their surrounds, the researcher said.
"The top five percent (of cities per population) could see increases in temperatures of about 8 C and larger," study co-author Francisco Estrada of the Institute for Environmental Studies in the Netherlands told  AFP.
Estrada and a team used different projections of average planetary warming, combined with the UHI effect and potential harms, to estimate the future costs of warming on cities.
The median city, right in the middle of the range, stands to lose between 1.4 and 1.7 percent of GDP per year by 2050 and between 2.3 and 5.6 percent by 2100, they concluded. "For the worst-off city, losses could reach up to 10.9 percent of GDP by 2100," wrote the team.
UHI "significantly" increases city temperatures and economic losses from global warming, they added. This meant that local actions to reduce UHI — such as planting more trees or cooling roofs and pavements, can make a big difference in limiting warming and minimising costs.
Cities cover only about one percent of earth's surface but produce about 80 percent of gross world product and account for around 78 percent of energy consumed worldwide, said the researchers. They produce more than 60 percent of global carbon dioxide emissions from burning coal, oil and gas for fuel.
The world's nations agreed in Paris in 2015 to the goal of limiting average global warming to two degrees Celsius over pre-Industrial revolution levels by curbing greenhouse gas levels in Earth's atmosphere. For the latest study, researchers used data from the world's 1,692 largest cities for the period 1950 to 2015.
A report by a leading research body monitoring the Arctic has found that previous projections of global sea level rise for the end of the century could be too low, thanks in part to the pace of ice loss of Arctic glaciers and the vast ice sheet of Greenland. It’s just the latest in a string of cases in which scientists have published numbers that suggest a grimmer picture than the one presented in 2013 by an influential United Nations body, the Intergovernmental Panel on Climate Change.
The assessment found that under a relatively moderate global warming scenario — one that slightly exceeds the temperature targets contained in the Paris climate agreement — seas could be expected to rise ‘‘at least’’ 1.7 feet by the year 2100. Under a more extreme, ‘‘business as usual’’ warming scenario, meanwhile, the minimum rise would be 2.4 feet.
The new findings were published as part of a broader overview report by the Arctic Monitoring and Assessment Program, a working group of the intergovernmental Arctic Council, which unites eight Arctic nations, including the United States, and six organizations representing the indigenous peoples of the Arctic. It is the work of 90 scientists and 28 peer reviewers.
The report bluntly contrasts its sea level findings with a previous 2013 report from the UN Intergovernmental Panel on Climate Change, which had put the ‘‘likely’’ low end sea level rise number for these two scenarios at about 1 foot and 1.5 feet for the period between 2081 and 2100. That global body — whose high-end sea level rise number for the year 2100 was just shy of 3.2 feet — has often seen its assertions on sea level rise faulted by scientists for being too conservative.
An influential study of Antarctica published last year in the journal Nature suggested that the frozen continent alone could nearly double the IPCC’s sea level projections for the end of the century.
(The IPCC did concede that sea levels could be higher than its ‘‘likely’’ forecast in the event of a ‘‘collapse of marine-based sectors of the Antarctic ice sheet’’ — but it added that ‘‘there is medium confidence that this additional contribution would not exceed several tenths of a meter of sea level rise during the 21st century.”)
And since then, several other scientific documents — presumably aware of this Antarctic research — have cited the possibility of particularly extreme sea level rise by 2100, even if they cannot necessarily quantify the likelihood of it occurring.
 ‘‘These estimates of higher sea level contributions from the Arctic will only add to the new, higher estimates of potential sea level contributions from Antarctica — which is not good news,’’ said Rob DeConto, a geoscientist at the University of Massachusetts at Amherst who published the aforementioned Antarctica study and also worked on the California study. He was not involved in the new Arctic report.
The Arctic report states that Greenland, in particular, lost 375 billion tons of ice per year from 2011 through 2014, enough to single-handedly raise the global sea level by about a millimeter per year. That annual loss, the document states, is ‘‘equivalent to a block of ice measuring 7.5 kilometers or 4.6 miles on all sides.’’
Because of the difference between the worst case and more moderate sea level rise scenarios, the report concludes that the Paris climate agreement could substantially reduce the global sea level rise seen by 2100, even though seas will still rise considerably under any scenario.
‘‘You have to have a deliberate and sustained implementation of Paris for 30 years before you see a significant difference in the rate of global sea level rise,’’ Colgan said.
The Trump administration’s irresponsible decision of withdrawing from Paris accord would make the situation worse and push the world closely to the biggest catastrophe in the humankind’s history. How can they continue calling for human rights and democracy while they are getting more extreme and conservative in protecting their benefits with the selfish policy of “America first”./.

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All comments [ 5 ]

John Smith 9/6/17 21:48

Warmer temperature would bring greater impacts on society, in terms of a rise in sea level, heat waves, droughts and other threats.

Deck Hero14 9/6/17 21:49

Such a rise – which would be much higher nearer the poles – would have cataclysmic and irreversible consequences for the Earth, making large parts of the planet uninhabitable and threatening the basis of human civilisation.

Jane smartnic 9/6/17 22:01

Part of once temperate regions could become uninhabitable, while humans fight each other for the world’s remaining resources.

Pack Cassiopian 9/6/17 22:02

If we do nothing to reduce this threat, where will the tipping point be that may mean we are no longer able to stop global warming?

Love Peace 9/6/17 22:04

With the tropics too hot to grow crops, and the sub-tropics too dry, billions of people would find themselves in areas of the planet which are essentially uninhabitable.

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