Climate change has increased the severity of drought in Australia’s Murray Darling Basin

 

drought36month1019

Parts of Australia’s Murray Darling Basin have had their driest 36 months on record, to 31 October 2019.  There has been some rain at the start of November 2019, so across the whole basin it may not be the driest three consecutive calendar years on record.

The record was set in the years 1965 to 1967.

There is, however, a factor which makes the current drought far worse than the 1965 to 1967 drought.  Summer temperatures are now far hotter in the Basin.  As shown in the chart below, mean summer temperatures during the 1965 to 1967 drought were less than one degree C hotter than the 1961 to 1990 average.  The last three summers have had mean summer temperatures more that 2 degrees C hotter and the 2018-19 summer was more than three degrees hotter!

tmean.mdb.1202.52151

The current drought is much more severe than the 1965 to 1967 drought due to climate change increasing evaporation.

The Murray Darling Basin is often referred to as Australia’s food bowl and accordingly food production is down which is costly to the economy and disastrous for the communities affected.  The federal government is pouring in billions of dollars in assistance, while still proclaiming at the United Nations that Australia is pulling our weight on actions to limit climate change.

Australia must do much more and must encourage other countries, especially the USA, to do likewise, because Australia is experiencing the costly effects of climate change.

In a future post I’ll write about what Australia should, and can, do to limit rising temperature and stimulate more rainfall.

Charlie Nelson

 

 

 

An inconvenient hot summer in Australia

With record high temperatures across much of the continent, smashing the previous record; with record rainfall in North Queensland and 500,000 cattle lost; with extreme drought in many locations, including the death of millions of fish in the Menindie Lakes; it has been a summer well beyond past experience.  Bushfires have caused loss of property in Tasmania, Victoria, and New South Wales.

With such an extreme summer being closely followed by a federal election, denial of climate change; claiming that Australia should do nothing as we are a small emitter of greenhouse gasses on a global scale; and token policies will not resonate well with the majority of the electorate.  As Australia is being damaged by climate change, and the damage will escalate, it is time to consider what action we can take which is of greater influence on global greenhouse gas emissions than our proportion of emissions.

Australia’s 2018-19 summer was very hot compared with all previous summers, dating back to 2010-11 (Chart 1).

Chart 1
hottestsummer01

The record mean temperature in 2018-19 was 0.86 degrees C hotter than the previous record set in 2013.  This margin is the greatest on record, exceeding the margin of 0.52 degrees C by which the summer of 1972-73 was hotter than the previous record in 1938-39 and 1925-26.

The only comparable extreme is the very low mean temperature in 1916-17.  That was during an extreme La Nina, but there was no extreme El Nino in 2018-19.

The temperatures shown in Chart 1 are relative to the average of the period 1961 to 1990 (27.5 degrees C).

The upwards trend is 1.3 degrees per century (Chart 2) and has accelerated to 2.2 degrees per century from 1970 (the last seven summers have been hotter than the 109 year trend).  These trends are highly statistically significant.

Chart 2
chart2

The trend mean temperature anomaly for 2019-20 is predicted to be 0.64 degrees, with a 95% confidence interval of 0.45 to 0.83.

The mean temperature anomaly relative to 1961 to 1990 across Australia in the summer of 2018-19 is shown in Chart 3.  Much of the continent was more than one degree hotter than the 1961 to 1990 average, many locations had a mean temperature more than 2 degrees hotter, and some places were more than 3 degrees hotter (the average was 2.1 degrees across the continent).

Chart 3
hottestsummer03

The record rainfall in much of north Queensland was in marked contrast to a dry summer in most of the rest of the continent (Chart 4).  This chart shows rainfall anomalies relative to the 1961 to 1990 average.

Chart 4
hottestsummer04

The longest continuous tracking of the general public’s level of belief in imminent global warming has been carried out by foreseechange (Chart 5).  The estimated likelihood of clear signs of global warming in the year ahead is a 63% chance, back to the level of 2007 when the electorate last voted the coalition out of office.  The last update of this tracking survey was in November 2018 – since then we have experienced the highly extreme summer of 2018-19, which would have further lifted the level of belief in imminent climate change.

Chart 5
chart5

Previous variations in the level of belief in imminent climate change have been caused, in part, by preceding temperatures and rainfall.

When the general public was asked to rate issues on the basis of the level of concern in the foreseeable future, climate change ranked fifth, ahead of traffic congestion, health, and crime (Chart 6).  The scale was from 0 (will not be at all concerned) to 10 (will be extremely concerned).  This survey was conducted in November 2018 and it is likely that the extreme summer of 2018-19 will have lifted the level of future concern about climate change.

Chart 6
chart6

In the lead-up to the imminent federal election, the electorate will be looking for a credible, urgent plan to mitigate climate change.

Australia must move on from the seemingly endless debate about whether human activity is causing climate change and whether we should do anything at all because our contribution to greenhouse gas emissions is less than 2% of the global total.

Australia can have an impact beyond our share and it is in our interests to do so given the economic and environmental damage we are experiencing and the economic opportunities we can capitalise on.  That will be the subject of a future article.

Charlie Nelson

 

 

Melbourne’s abrupt loss of rainfall

Melbourne’s rainfall has abruptly fallen by an average of 107mm per year from 1997 (Chart 1).

Chart 1
melbmean

There are still some quite wet years (2010 and 2011) and there have been very few dry years (1997 was the second driest on record.  The average has just suddenly dropped.

A seven year moving average reveals the existence of rainfall cycles over Melbourne (Chart 2).

Chart 2
melbma7

To some degree, less rainfall is an expected consequence of climate change – the sub-tropical high pressure ridge is expected to move further south towards Melbourne (the deserts extend southwards).  But the change has been a  downwards step change rather than a trend.

There are natural cycles in rainfall in south eastern Australia and these have played a major part in the loss of rainfall from 1996.  The relative contributions of climate change and natural cycles are not clear as yet.  I was able to advise the Victorian Minister for water, in 2011 during the most recent wet period, that there would be another severe drought from 2017 to 2022.  That prediction, so long in advance, looks as though it was accurate.

I will provide an update in early 2020.

Charlie Nelson