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The complete story of climate change requires the long view

The pie chart shows relative contributions to global warming divided into the world's regions. The enlargements represent the growth of the total cumulative global radiation fluctuation. CRF is cumulative radiation fluctuation. RCP is representative concentration path or a modeled emission scenario based on previous inputs. RCP 2.6 is about what was agreed under the Intercontinental Panel on Climate Change 2015, the "Paris Agreement", where nations agreed to limit global warming to 1.5 degrees Celsius in this century. RCP 8.5 is business as usual, with increasing emissions. Credit: A.R. Ravishankara / Colorado State UniversityScience is clear that human activities in the last century have contributed to the greenhouse effect being heated by the earth's surface. Much of the global climate change conversation fixes which individual countries or regions contribute to the problem, and what to do (or not) to reverse the tide. But Colorado State University's A.R. Ravishankara, University Distinguished Professor who holds joint appointments in chemistry and atmospheric departments, says the whole picture is longer and more complex than meets the eye. It is a legacy of past acts, as well as irrevocable commitments for the future. Ravishankara and co-author Daniel Murphy of the National Oceanic and Atmospheric Administration offer a new estimate that gives the long perception of which nine different world regions have contributed to climate change since 1900. They also show how this division is likely to look 2100 under different emission scenarios. Their study is in the Proceedings of the National Academy of Sciences December 17th.…



The pie chart shows relative contributions to global warming divided into the world’s regions. The enlargements represent the growth of the total cumulative global radiation fluctuation. CRF is cumulative radiation fluctuation. RCP is representative concentration path or a modeled emission scenario based on previous inputs. RCP 2.6 is about what was agreed under the Intercontinental Panel on Climate Change 2015, the “Paris Agreement”, where nations agreed to limit global warming to 1.5 degrees Celsius in this century. RCP 8.5 is business as usual, with increasing emissions. Credit: A.R. Ravishankara / Colorado State University

Science is clear that human activities in the last century have contributed to the greenhouse effect being heated by the earth’s surface. Much of the global climate change conversation fixes which individual countries or regions contribute to the problem, and what to do (or not) to reverse the tide.

But Colorado State University’s A.R. Ravishankara, University Distinguished Professor who holds joint appointments in chemistry and atmospheric departments, says the whole picture is longer and more complex than meets the eye. It is a legacy of past acts, as well as irrevocable commitments for the future.

Ravishankara and co-author Daniel Murphy of the National Oceanic and Atmospheric Administration offer a new estimate that gives the long perception of which nine different world regions have contributed to climate change since 1900. They also show how this division is likely to look 2100 under different emission scenarios. Their study is in the Proceedings of the National Academy of Sciences December 17th.

They call their calculation “cumulative radiation fluctuation” because it integrates the ebb and flow of climate factors in the last century, rather than just a snapshot of what it is today. “Radiative Forcement” is a metric that measures the solar energy retained by the earth. Global warming is the result of positive radiation fluctuation, or more energy is retained by the Earth than flying back into space.

Their investigation also underscores the dirty two-sided role of particulate pollutants in the atmosphere, the result of burning fossil fuels, fires and other human activities that have spun contaminants and dust in the atmosphere for many decades. Such aerosols are short-lived in the atmosphere, but they have a cooling effect due to their interaction with sunlight and clouds. While carbon dioxide and other greenhouse gases remain in the atmosphere and continue to contribute to heating for many years, aerosols spread with their net cooling effects are spread more quickly. In total, the presence of aerosols has masked some of the effects of global warming.

In its analysis, researchers found that, for example, between 1910 and 2017, China, Europe and North America had periods of almost no network contribution to heating. These periods were characterized by rapid industrialization and GDP growth when fossil fuel emissions increased, but few air quality controls were carried out. The study further shows that each region’s contribution to radiation pressure due to carbon dioxide (and other greenhouse gases) emissions from 2018 to 2100 will be greater than the total warming that contributed in the last century.

“So far China has contributed very little,” said Ravishankara. “China has mainly paid for its carbon dioxide emissions through poor air quality.”

However, as China implements clean air standards ahead and the country’s emissions increase slower, the share of contributions to climate change will increase, according to the study. North America is the largest contributor now and will remain so through 2100.

The double-sided coin of aerosols-short-lived cooling but harmful to human health-is strongly illustrated in a separate study written by CSU’s postdoctoral researcher Liji David, Ravishankara and other colleagues, to be published online in GeoHealth. Researchers estimate that more than 1 million premature deaths per year in India are due to “surrounding particulate air pollutants in the form of respiratory particles such as sulphate aerosols, dust and soot. In India, the use of biomass in homes for heating and cooking is the dominant contributor to it here for early mortality.

Of the estimated 1.1 million for early deaths in 2012 from small particles in India, about 60 percent were due to anthropogenic pollutants released in the region, according to the study.

India’s contribution to climate change has so far been minimal, which Murphy and Ravishankara showed in PNAS, as it will be even 2100 compared to other nations. Since India is conducting clean air policy and working to reduce premature deaths from air pollution, its role in climate change may increase due to aerosols plays less role to come penalize climate change, but human health will be improved.

Ravishankara emphasizes that people should look at the effects of emissions holistically. Future climate scenarios must take into account all the heating contributions so far and the impact of these contributions forward. Emission reductions would not only help the climate, but also human health, he says. Aggressively reduced carbon dioxide and other emissions, for planet and human health, are the only viable alternatives.

“We do not just need to ask what our commitment is going forward but what’s our heritage?” Ravishankara said.


Explore further:
The impact of particulate pollution varies greatly depending on where it originated

More information:
D. M. Murphy et al., “Trends and Patterns in Contribution to Cumulative Radiation Stumbling from Different Regions in the World” PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1813951115

Journal Reference:
Negotiations by the National Academy of Sciences

Provided by:
Colorado State University

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