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Paris emis­sions reduc­tion pledges reduce risks of severe warm­ing, study shows

pub­lished 29 Novem­ber 2015 | mod­i­fied 29 Novem­ber 2015

COP21 logoMore than 190 coun­tries are meet­ing in Paris next week in the COP21 to cre­ate a durable frame­work for address­ing cli­mate change and to imple­ment a process to reduce green­house gases over time. A key part of this agree­ment would be the pledges made by indi­vid­ual coun­tries to reduce their emissions.

A study pub­lished online on 26 Novem­ber in Sci­ence shows that if imple­mented and fol­lowed by mea­sures of equal or greater ambi­tion, the Paris pledges have the poten­tial to reduce the prob­a­bil­ity of the high­est lev­els of warm­ing, and increase the prob­a­bil­ity of lim­it­ing global warm­ing to 2 degrees Celsius.

In the lead up to the Paris meet­ings, coun­tries have announced the con­tri­bu­tions that they are will­ing to make to com­bat global cli­mate change, based on their own national cir­cum­stances. These Intended Nation­ally Deter­mined Con­tri­bu­tions, or INDCs, take many dif­fer­ent forms and extend through 2025 or 2030.

Exam­ples of these com­mit­ments include the United States’ vow to reduce emis­sions in 2025 by 2628 per­cent of 2005 lev­els and China’s pledge to peak emis­sions by 2030 and increase its share of non-​fossil fuels in pri­mary energy con­sump­tion to around 20 per­cent. In the study, the sci­en­tists tal­lied up these INDCs and sim­u­lated the range of tem­per­a­ture out­comes the result­ing emis­sions would bring in 2100 under dif­fer­ent assump­tions about pos­si­ble emis­sions reduc­tions beyond 2030.

We analysed not only what the com­mit­ments would achieve over the next ten to fif­teen years, but also how they might lay a foun­da­tion for the future.
Allen Faw­cett, lead author, U.S. Envi­ron­men­tal Pro­tec­tion Agency »

We wanted to know how the com­mit­ments would play out from a risk man­age­ment per­spec­tive,” said econ­o­mist Fawcett.

Although many researchers have focused on the impor­tance of the 2 degree limit, Faw­cett and col­leagues assessed uncer­tainty in the cli­mate change sys­tem from an over­all risk man­age­ment per­spec­tive. They analysed the full range of tem­per­a­tures the INDCs might attain, and deter­mined the odds for achiev­ing each of those tem­per­a­tures. To deter­mine odds, they mod­elled the future cli­mate hun­dreds of times to find the range of tem­per­a­tures these var­i­ous con­di­tions produce.

An exam­ple of what might be the effect of cli­mate change can be seen in this time-​lapse video of ice melt­ing of the Menden­hall glac­ier in Alaska, by Extreme Ice Sur­vey:

Time-​lapse video of Alaska’s Menden­hall glac­ier. You’ll see that the glac­ier “deflates”— like air releas­ing from a bal­loon. Notice how ice melts at the glacier’s edge, while thin­ning at the same time.

It’s not just about 2 degrees,” said Gokul Iyer, the study’s lead sci­en­tist at the Joint Global Change Research Insti­tute, a col­lab­o­ra­tion between the Depart­ment of Energy’s Pacific North­west National Lab­o­ra­tory and the Uni­ver­sity of Mary­land. “It is also impor­tant to under­stand what the INDCs imply for the worst lev­els of cli­mate change.”

In the study, the sci­en­tists com­pare the Paris com­mit­ments to a world in which coun­tries don’t act at all or start reduc­ing green­house gas emis­sions only in 2030.

The team found that if coun­tries do noth­ing to reduce emis­sions, the earth has almost no chance of stay­ing under the 2 degree limit, and it is likely that the tem­per­a­ture increase would exceed 4 degrees. They went on to show that the INDCs and the future abate­ment enabled by Paris intro­duce a chance of meet­ing the 2 degree tar­get, and greatly reduce the chance that warm­ing exceeds 4 degrees. The extent to which the odds are improved depends on how much emis­sions lim­its are tight­ened in future pledges after 2030.

Long-​term tem­per­a­ture out­comes crit­i­cally hinge on emis­sions reduc­tion efforts beyond 2030,” said Iyer. “If coun­tries imple­ment their INDCs through 2030 and ramp up efforts beyond 2030, we’ll have a much bet­ter chance of avoid­ing extreme warm­ing and keep­ing tem­per­a­ture change below 2 degrees Cel­sius. It’s impor­tant to know that the INDCs are a step­ping stone to what we can do in the future.”

How they did it
To per­form the analy­sis, the team incor­po­rated the INDCs along with assump­tions about future emis­sions reduc­tions into a global, tech­no­log­i­cally detailed model of the world called the Global Change Assess­ment Model or GCAM that includes energy, econ­omy, agri­cul­ture and other sys­tems. The GCAM model pro­duced num­bers for global green­house gas emis­sions, which the team then fed into a cli­mate model called Model for the Assess­ment of Greenhouse-​gas Induced Cli­mate Change or MAG­ICC. Run­ning the sim­u­la­tions for each sce­nario 600 times resulted in a range of tem­per­a­tures for the year 2100, which the team con­verted into probabilities.

What’s next
Iyer said the next thing to look at is the ques­tion of the kinds of poli­cies and insti­tu­tional frame­works that could pave the way for a robust process that enables emis­sions reduc­tion efforts to pro­gres­sively increase over time.

(Source: Pacific North­west National Lab­o­ra­tory news release, 26.11.2015)

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