BAMOS
Sept 2017
The likelihood of winter warmth like this
year is rising. Best estimate chances
are shown with the vertical black lines
showing the 90% confidence interval.
highs for maximum temperatures a remarkable ten times so far
this century (across summer, autumn, winter and spring). The
increased frequency of heat records in Australia has already
been linked to climate change. More winter warmth to come
The record winter warmth is part of a long-term upward trend
in Australian winter temperatures. This prompts the question:
how much has human-caused climate change altered the
likelihood of extremely warm winters in Australia? Under the Paris Agreement, the world’s nations are aiming to
limit global warming to below 2 ºC above pre-industrial levels,
with another more ambitious goal of 1.5 ºC as well. These targets
are designed to prevent the worst potential impacts of climate
change. We are currently at around 1 ºC of global warming.
I used a standard event attribution methodology to estimate
the role of climate change in this event.
I took the same simulations that the Intergovernmental Panel on
Climate Change (IPCC) uses in its assessments of the changing
climate, and I put them into two sets: one that represents
the climate of today (including the effects of greenhouse gas
emissions) and one with simulations representing an alternative
world that excludes our influences on the climate.
I used 14 climate models in total, giving me hundreds of
years in each of my two groups to study Australian winter
temperatures. I then compared the likelihood of record warm
winter temperatures like 2017 in those different groups. You can
find more details of my method here.
I found a stark difference in the chance of record warm winters
across Australia between these two sets of model simulations.
By my calculations there has been at least a 60-fold increase in
the likelihood of a record warm winter that can be attributed
to human-caused climate change. The human influence on
the climate has increased Australia’s temperatures during the
warmest winters by close to 1 ºC.
Looking ahead, it’s likely we’re going to see more record warm
winters, like we’ve seen this year, as the climate continues to
warm.
Even if global warming is limited to either of these levels, we
would see more winter warmth like 2017. In fact, under the 2 ºC
target, we would likely see these winters occurring in more than
50% of years. The record-setting heat of today would be roughly
the average climate of a 2 ºC warmed world.
While many people will have enjoyed the unusual winter
warmth, it poses risks for the future. Many farmers are struggling
with the lack of reliable rainfall, and bad bushfire conditions are
forecast for the coming months. More winters like this in the
future will not be welcomed by those who have to deal with the
consequences.
Climate data provided by the Bureau of Meteorology. For more
details about winter 2017, see the Bureau’s Climate Summaries.
You can find more details on the specific methods applied for this
analysis here.
Article originally published in The Conversation, 1 September 2017.
15