On November 5, NOAA released its fourth special issue of the Bulletin of the American Meteorological Society, featuring the research of 32 groups of scientists that investigated 28 extreme weather events in 2014 to determine the degree to which natural variability and human-caused climate change played a role.
Included in the report are studies that find climate change has increased long-term fire risk in California and made the Hawaiian hurricane season substantially more likely. Globally, the report provides overwhelming evidence that climate change influenced the likelihood and intensity of heat extremes. Specific 2014 extremes linked to climate change include the devastating floods in Jakarta, the increased frequency and severity of heat waves across Australia, the drought in East Africa, and the extreme Himalayan snowstorm.
That scientists are able to directly connect human-caused warming to the likelihood or severity of extreme events underscores the recent advancement in climate attribution science. Scientists once hesitated to connect present-day extreme weather events to climate change, instead focusing on long-term trends and future projections. The reports of the foremost climate science institution, the Intergovernmental Panel on Climate Change, primarily present trends discernible across time and space, like the global increase in extreme precipitation and heat waves. We now know that climate change is worsening specific extreme events, with both economic and human consequences.
Approximately half of the studies in the BAMS special report identify a clear climate change influence distinct from natural variability, which is always part of any weather and climate extreme. As for the half that didn’t, failing to identify a climate change connection does not necessarily mean climate had no influence. The authors of the report point to three reasons that could explain the absence of a clear climate change connection: (1) there was no human influence on the event, (2) the studies were not comprehensive and factors not considered by the studies may have been influenced by climate change, and (3) the human influence could not be identified with the scientific tools available today.
Overall the report provides new evidence towards the strengthening scientific case connecting climate change with many types of extreme weather. Experts are available for additional commentary, and can help with untangling the many implications of the report.