Environment
Published:
Tuesday October 8, 2013 MYT 12:00:00 AM
Updated: Tuesday October 8, 2013 MYT 7:09:29 AM THE STAR
Environmental effects:
It's our doing
Floods hit Shantou in southern China’s
Guangdong
province. Climate change is causing more extreme weather events such as
heatwaves, storms and droughts. – AFP
Human activity is the dominant
cause of global warming observed since the 1950s, and scientists predict
temperatures will rise another 0.3˚C to 4.8˚C this century.
THE world’s leading climate scientists have
for the first time established a limit on the amount of greenhouse gases that
can be released before the Earth reaches a tipping point and predicted that it
will be surpassed within decades unless swift action is taken to curb the
current pace of emissions.
The warning was issued recently by a panel of United
Nations-appointed climate change experts meeting in Stockholm, Sweden.
The Intergovernmental Panel on Climate Change (IPCC) estimated that once a
total of one trillion tonnes of carbon dioxide are emitted into the atmosphere,
the planet will exceed 2°C of warming, the internationally agreed-upon
threshold to the worst effects of climate change.
“We’ve burned through half that amount” since
pre-industrial times, Michael Oppenheimer, a professor of geosciences and
international affairs at Princeton University who reviewed the report and is a
co-author of the panel’s upcoming report on the effect of climate change, said.
alt="People scream outside the United Nation¿s Intergovernmental Panel on Climate Change (IPCC) to demand immediate political action on Climate debate on September 27, 2013 in Stockholm. The panel said it was more certain than ever that humans were the cause of global warming and predicted temperatures would rise another 0.3 to 4.8 degrees Celsius this century. AFP PHOTO/JONATHAN NACKSTRAND"
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Act now: Activists protesting during
the recent Intergovernmental Panel on Climate Change meeting in Stockholm, Sweden,
demanding for immediate political action on global warming. – AFP
“Because the rates of emissions are growing,
it looks like we could burn through the other half in the next 25 years” under
one of the more dire scenarios outlined in the report.
Other scenarios show that the threshold will
be reached later this century. The finding constitutes a warning to governments
to cut emissions of carbon dioxide, the main greenhouse gas, which is generated
by the burning of fossil fuels, industrial activity and deforestation.
Calling climate change “the greatest challenge
of our time,” panel co-chair Thomas Stocker said humankind’s fate in the next
100 years “depends crucially on how much carbon dioxide will be emitted in the
future”.
In the report, the panel said it is 95%
certain that human activity is the dominant cause of the global warming
observed since the 1950s. That is up from 90% six years ago.
“Human influence has been detected in warming
of the atmosphere and the ocean, in changes in the global water cycle, in
reductions in snow and ice, in global mean sea level rise, and in changes in
some climate extremes,” the report said.
The report is the panel’s fifth major
assessment since 1990. It reaffirms many of the conclusions of past reports,
but with greater confidence.
“The atmosphere and ocean have warmed, the
amounts of snow and ice have diminished, sea level has risen and the concentrations
of greenhouse gases have increased,” the panel wrote in a 36-page summary of
its findings.
“Each of
the last three decades has been successively warmer at the Earth’s surface than
any preceding decade since 1850.”
The report also addressed the so-called
hiatus, a slowdown in the rise of surface temperature that has been observed
over the last 15 years. That slowing of the increase in temperatures has been
seized on by sceptics to cast doubt on the science of climate change. The
report touches the subject only briefly, saying that temperatures fluctuate
naturally in the short term and “do not in general reflect long-term climate
trends”.
Brenda Ekwurzel, a climate scientist for the
Union of Concerned Scientists, said the slowdown is more like a speed bump, a
result of heat being trapped and circulated through the ocean and atmosphere in
different ways rather than a fundamental change in the climate. She said
surface temperature is just one of many expressions of climate change,
including sea level rise, melting ice and ocean acidification.
“The global average temperature is one kind of
a thermometer, but an even bigger thermometer is the ocean, which is absorbing
most of the excess heat that climate change is creating,” she said.
The report updates predictions of how
temperature and sea level are expected to rise over the century.
The panel now expects sea level to rise
globally by 26cm and 82cm by century’s end, up from the rise of 17cm to 57cm it
projected in 2007.
Those figures now include the contribution of
massive ice sheets in Antarctica and Greenland
that are creeping toward the ocean as they melt. The panel failed to account
for that variable in its previous report, prompting criticism from the
scientific community that its previous sea level rise projections were too low.
The panel also lowered the bottom of the range
of temperature increase expected over the long term if carbon dioxide
concentrations in the atmosphere double. The planet would warm by at least
1.5°C even if aggressive action is taken to cut emissions, but temperatures
could rise as much as 4.5°C in other scenarios.
“If no action is taken, no way will you be in
the lower band,” Michel Jarraud, secretary-general of the UN’s World
Meteorological Organisation said.
Environmental activists greeted the report
with calls for government action.
“This IPCC climate science assessment tells us
in the strongest possible terms that we ignore climate change at our great
peril,” said Earthjustice president Trip Van Noppen.
The assessment was written by more than 800
scientists from around the world. The panel does not conduct its own research,
but collects and summarises thousands of peer-reviewed scientific studies. The
report will inform negotiations toward a new international climate treaty to
cut greenhouse gas emissions that is supposed to be reached by 2015. – Los Angeles Times/McClatchy-Tribune
Information Services
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WARMING of the climate system is unequivocal, and
since the 1950s, many of the observed changes are unprecedented over decades to
millennia.
The atmosphere and ocean have warmed, the amounts of
snow and ice have diminished, sea level has risen and the concentrations of
greenhouse gases have increased. Human influence on the climate system is
clear. Limiting climate change will require substantial and sustained
reductions of greenhouse gas emissions.
It is extremely likely that human influence has been
the dominant cause of the observed warming since the mid-20th century. Each of
the last three decades has been successively warmer at the Earth’s surface than
any preceding decade since 1850. In the northern hemisphere, 1983-2012 was
likely the warmest period of the last 1,400 years. Warming since 1951 has been
about 0.12°C per decade. This slowed over the past 15 years to 0.05°C per decade,
but the time scale is too short to read anything into that yet.
Extreme events
Changes in many extreme weather and climate events
have been observed since about 1950. The number of cold days and nights has
decreased, and number of warm days and nights has increased. It is likely that
the frequency of heatwaves has increased in large parts of Europe, Asia and Australia. The
frequency or intensity of heavy precipitation events has likely increased in
North America and Europe.
Ocean warming
The ocean stored more than 90% of the energy
accumulated between 1971 and 2010. It is virtually certain that the upper ocean
(0-700m) warmed from 1971 to 2010 and it likely warmed between the 1870s and
1971.
Ice
Over the last two decades, the Greenland and Antarctic
ice sheets have been losing mass, glaciers have continued to shrink almost
worldwide, and Arctic sea ice and northern hemisphere spring snow cover have
continued to decrease in extent. Loss of Greenland’s
icesheet has likely increased from 34 billion tonnes per year in the decade to
2001 to 215 billion tonnes a year over the following decade.
In Antarctica, the rate of loss likely increased from
30 billion tonnes a year to 147 billion tonnes a year over the same time scale,
mainly from the northern Antarctic peninsula and the Amundsen Sea sector of West Antarctica.
Arctic sea ice contracted at a rate as high as 4.1% a
decade from 1979 to 2012; there has been shrinkage of summer ice extent every
season and in every successive decade. But Antarctic sea ice “very likely”
increased by up to 1.8% per decade during the same period.
Snow cover has been retreating in the northern
hemisphere since the mid-20th century. There has also been a “considerable
reduction” in the thickness and extent of Siberian permafrost over the last
three decades.
Sea level
The global mean sea level rose by 19cm from 1901-2010,
an average 1.7mm per year. This accelerated to 3.2mm per year between 1993 and
2010. During the last period between Ice Ages, when temperatures were lower
than those mostly projected for 2100, the maximum sea level was at least 5m
higher than present, due to meltwater from Greenland but also from Antarctica.
Glacier loss and ocean thermal expansion account for about 75% of observed sea
level rise since the early 1970s.
Greenhouse gas levels
The atmospheric concentrations of carbon dioxide
(CO2), methane and nitrous oxide have increased to levels unprecedented in at
least the last 800,000 years. CO2 concentrations have increased by 40% since
pre-industrial times, primarily from fossil-fuel emissions and secondly from
net land-use change emissions.
In 2011, levels of CO2, the main greenhouse gas, stood
at 391 parts per million (ppm) in the atmosphere, a rise of about 40% over
pre-industrial levels. Up to 2011, total man-made emissions of CO2 since
industrialisation were 545 billion tonnes of carbon. CO2 from fossil fuels and
cements amounted to 365 billion tonnes of carbon. Deforestation and other land
use accounted for 180 billion tonnes. The ocean has absorbed 155 billion
tonnes; natural terrestrial systems 150 billion; 240 billion are in the
atmosphere. CO2 uptake by the sea very likely results in acidification of the
ocean.
The future (to 2100)
The most optimistic of four warming scenarios sees an
average temperature rise of 1°C by 2100 over 2000 levels, ranging from 0.3°C to
1.7°C. This is the only scenario that can safely meet the UN’s target of 2°C.
By comparison, the worst scenario has an average warming this century of 3.7°C,
ranging from 2.6 °C to 4.8°C – a maximum many experts deem catastrophic.
2°C?
To have a good chance of meeting the UN target of
limiting man-made warming to less than 2°C compared to pre-industrial times,
all carbon emissions from man-made sources must be limited to about 1,000 billion
tonnes, or gigatonnes. An amount of 531 gigatonnes was already emitted by 2011.
Sea-level rise
The rate of sea level rise since the mid-19th century
has been larger than the mean rate during the previous two millennia. The
global mean sea level rose by around 19cm from 1901 to 2010 due to increased
ocean warming and melting glaciers and ice sheets. The rate of rise accelerated
between 1993 and 2010, and it is very likely to increase further during the
21st century and beyond. The report sees the following average rise in global
sea level: 17cm to 38cm by mid-century, and 26cm to 82cm by 2100.
Extreme weather events
Exceptional rainstorms are “very likely” to become
more intense and more frequent over mid-latitude countries and the wet tropics.
The area encompassed by the monsoon systems is likely to increase over the 21st
century, and monsoon rainfall is likely to intensify. The monsoon season is
likely to lengthen in many regions.
Ice cover
By 2100, year-round reductions in the extent of Arctic
sea ice are seen under all scenarios. They range from a shrinkage in summer sea
ice of 43% to 94% and in winter ice of 8% to 34%.
Beyond 2100
Most aspects of climate change will persist for many
centuries even if emissions of CO2 are stopped. This represents a substantial
multi-century commitment created by past, present and future emissions of CO2.
Depending on the scenario, about 15% to 40% of emitted
CO2 will remain in the atmosphere longer than 1,000 years.
Sea levels will rise for “many centuries” beyond 2100
due to thermal expansion. If CO2 stabilises below 500ppm, the rise is likely to
be less than 1m by 2300; but it will be up to 3m if CO2 concentrations are
beyond 700ppm. The rise would be higher in the event of “sustained mass loss”
by ice sheets.
The near-complete loss of the Greenland
ice sheet over a millennium or more would drive up the seas by up to 7m. Rough
estimates say the threshold for this is between 1°C and 4°C over pre-industrial
levels. – AFP
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