DOE/Lawrence Berkeley National Laboratory
A paper published this week during the American Geophysical Union (AGU) fall meeting in San Francisco points to new evidence of human influence on extreme weather events.
Three researchers from Lawrence Berkeley National Laboratory
(Berkeley Lab) are among the co-authors on the paper, which is included in
"Explaining Extreme Events of 2015 from a Climate Perspective," a
special edition of the Bulletin of the American Meteorological Society (BAMS)
released December 15 at the AGU meeting.
The paper, "The Deadly Combination of Heat and Humidity in India and Pakistan in Summer 2015," examined observational and simulated temperature and heat indexes, concluding that the heat waves in the two countries "were exacerbated by anthropogenic climate change."
While these countries typically experience severe heat in the summer, the 2015 heat waves -- which occurred in late May/early June in India and in late June/early July in Pakistan -- have been linked to the deaths of nearly 2,500 people in India and 2,000 in Pakistan.
"I was deeply moved by television coverage of the human
tragedy, particularly parents who lost young children," said Michael
Wehner, a climate researcher at Berkeley Lab and lead author on the paper, who
has studied extreme weather events and anthropogenic climate change
extensively.
This prompted him and collaborators from Berkeley Lab, the Indian Institute of Technology Delhi and UC Berkeley to investigate the cause of the 2015 heat waves and determine if the two separate meteorological events were somehow linked.
This prompted him and collaborators from Berkeley Lab, the Indian Institute of Technology Delhi and UC Berkeley to investigate the cause of the 2015 heat waves and determine if the two separate meteorological events were somehow linked.
They used simulations from the Community Atmospheric Model
version 5 (CAM5), the atmospheric component of the National Center for
Atmospheric Research's Community Earth System Model, performed by Berkeley Lab
for the C20C+ Detection and Attribution Project.
Current climate model-based products are not optimized for research on the attribution of the human influence on extreme weather in the context of long-term climate change; the C20C+ Detection and Attribution Project fills this gap by providing large ensembles of simulation data from climate models, running at relatively high spatial resolution.
Current climate model-based products are not optimized for research on the attribution of the human influence on extreme weather in the context of long-term climate change; the C20C+ Detection and Attribution Project fills this gap by providing large ensembles of simulation data from climate models, running at relatively high spatial resolution.
The experimental design described in the BAMS paper used
"factual" simulations of the world and compared them to
"counterfactual" simulations of the world that might have been had
humans not changed the composition of the atmosphere by emitting large amounts
of carbon dioxide, explained Dáithí Stone, a research scientist in Berkeley
Lab's Computational Research Division and second author on the BAMS paper.
"It is relatively common to run one or a few simulations of
a climate model within a certain set of conditions, with each simulation
differing just in the precise weather on the first day of the simulation; this
difference in the first day propagates through time, providing different
realizations of what the weather 'could have been,'" Stone said.
"The special thing about the simulations used here is that we ran a rather large number of them. This was important for studying a rare event; if it is rare, then you need a large amount of data in order to have it occurring frequently enough that you can understand it."
"The special thing about the simulations used here is that we ran a rather large number of them. This was important for studying a rare event; if it is rare, then you need a large amount of data in order to have it occurring frequently enough that you can understand it."
The researchers examined both observational and simulated
temperature alone as well as the heat index, a measure incorporating both
temperature and humidity effects. From a quality-controlled weather station
observational dataset, they found the potential for a very large, human-induced
increase in the likelihood of the magnitudes of the two heat waves. They then
examined the factual and counterfactual simulations to further investigate the
presence of a human influence.
"Observations suggested the human influence; simulations
confirmed it," Wehner said.
The research team also found that, despite being close in
location and time, the two heat waves were "meteorologically
independent." Even so, Wehner emphasized, "the India/Pakistan paper
confirms that the chances of deadly heat waves have been substantially
increased by human-induced climate change, and these chances will certainly
increase as the planet continues to warm."
Data from Berkeley Lab's simulations were also analyzed as part
of another study included in the special edition of BAMS released at the AGU
meeting. That study, "The Late Onset of the 2015 Wet Season in Nigeria,"
which was led by the Nigerian Meteorological Agency, explores the role of
greenhouse gas emissions in changing the chance of a late wet season, as
occurred over Nigeria in 2015.
"The C20C+ D&A Project is continuing to build its
collection of climate model data with the intention of supporting research like
this around the world," Stone said.
The C20C+ D&A portal is hosted and supported by Berkeley
Lab's National Energy Research Scientific Computing Center (NERSC), a DOE
Office of Science User Facility, and the simulations for the two papers were
run on NERSC's Hopper supercomputer, while the data analysis was done on
NERSC's Edison and Cori systems.
The simulations were conducted as part of a program dedicated to advancing our understanding of climate extremes and enhancing our ability to attribute and project changes in their risk because of anthropogenic climate change. The research was supported by the DOE Office of Science and the National Science Foundation.
The simulations were conducted as part of a program dedicated to advancing our understanding of climate extremes and enhancing our ability to attribute and project changes in their risk because of anthropogenic climate change. The research was supported by the DOE Office of Science and the National Science Foundation.
"Explaining Extreme Events of 2015 from a Climate
Perspective," a special edition of the Bulletin of the American
Meteorological Society, can be accessed here: http://www.ametsoc.org/ams/index.cfm/publications/bulletin-of-the-american-meteorological-society-bams/explaining-extreme-events-from-a-climate-perspective/