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Why 2℃ of global warming is much worse for Australia than 1.5℃

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The Conversation

Australia is a land of extremes. We’ve experienced all manner of climate extremes over the past few years, from heatwaves (both on land and over the Great Barrier Reef), to droughts and flooding rains.

We can already link some of these recent extreme events to climate change. But for others, the link is less clear.

So far we have had about 1℃ of global warming above the average pre-industrial climate. So how will extreme weather events change with more warming in the future? Will they become more frequent? Will they become more severe?

We have investigated these questions in our new research, published today in Nature Climate Change.

Climate targets

The Paris Agreement, brokered in 2015, committed the world’s governments to:

Holding the increase in the global average temperature to well below 2℃ above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5℃ above pre-industrial levels, recognising that this would significantly reduce the risks and impacts of climate change.

It is vital that we understand how climate extremes in Australia might change if we limit global warming to either 1.5℃ or 2℃, and what the implications might be of pursuing the more lenient target rather than the more ambitious one.

In our study we used state-of-the-art climate model simulations to examine the changing likelihood of different climate extremes under four different scenarios: a natural world without any human-caused climate change; the world of today; a 1.5℃ warmer world; and a 2℃ warmer one.

Heat extremes are here to stay

First, we looked at hot Australian summers, like the record-breaking “angry summer” of 2012-13.

We already knew that human influences on the climate had increased the likelihood of hot summers. Our results show that this trend would continue with future warming. In fact, in a world of 2℃ global warming, even an average summer would outstrip those historically hot ones like 2012-13.

Australian summer temperatures are strongly related to the El Niño-Southern Oscillation, with hot summers more likely to occur during El Niño events, and cooler ones during La Niña episodes.

In the past, a summer as hot as 2012-13 would have been very unlikely during a La Niña. But our modelling predicts that with either 1.5℃ or 2℃ of global warming, we could expect similarly angry summers to occur during both El Niño and La Niña periods.

We already know that the sea surface temperatures associated with mass bleaching of much of the Great Barrier Reef in early 2016 would have been virtually impossible without climate change. If the world continues to warm to either the 1.5℃ or 2℃ levels, very warm seas like we saw early last year would become the norm.

aus global warming chart

High sea temperatures linked to coral bleaching in Great Barrier Reef will become more likely in a warmer world

In fact, our research suggests that with 2℃ of global warming, the future average sea temperatures around the Great Barrier Reef would be even hotter than the extremes observed around the time of the 2016 bleaching.

Less change for heavy rains and droughts

In December 2010 Queensland was devastated by severe flooding following very heavy rainfall. Our analysis suggests that this kind of event is highly unusual, and may well continue to be so. There isn’t a clear signal for an increase or decrease in those events with ongoing climate warming.

Natural climate variability seems to play a greater role than human-driven climate change (at least below the 2℃ threshold) when it comes to influencing Australian heavy rainfall events.

The Millennium Drought across southeast Australia led to water shortages and crop failures. Drought is primarily driven by a lack of rainfall, but warmer temperatures can exacerbate drought impacts by increasing evaporation.

Our results showed that climate change is increasing the likelihood of hot and dry years like we saw in 2006 across southeast Australia. At 1.5℃ and 2℃ of global warming these events would probably be more frequent than they are in today’s world.

aus weather extreme chart

Heat extremes are much more common at 2℃ than 1.5℃

Not a lost cause

It is clear that Australia is going to suffer from more frequent and more intense climate extremes as the world warms towards (and very likely beyond) the levels described in the Paris Agreement.

If we miss these targets, the warming will continue and the extremes we experience in Australia are going to be even worse.

With either 1.5℃ or 2℃ global warming, we will see more extremely hot summers across Australia, more frequent marine heatwaves of the kind that can cause bleaching of the Great Barrier Reef, and probably more frequent drought conditions too.

The more warming we experience, the worse the impacts will be. The solution is clear. To limit global warming, the world’s nations need to reduce their greenhouse gas emissions – fast.

Source:The Conversation. Reproduced with permission.  

  • DogzOwn

    Thank you to authors. What will it take for this to be understood by economists? Do they need % numbers converted to Basis Points, bookies odds, fractions…or what? How much longer can they get away with saying, not yet, we can’t afford to take any action?

  • Rick Kooi

    1799
    “Climate Change was theorized in 1799, Alexander von Humboldt.”
    .
    1827
    “Climate Changed Scientifically tied to Global Warming & Human Activity by physicist & astronomer Simeon Denis Poisson, 1811-1827.”
    .
    He lectured, extensively, on this threat by 1827 !
    .
    1847
    “George Perkins Marsh (1801-1882) author of the 1847 lecture that predicted > “human-induced climate change.” <
    .
    THEY WERE ALREADY LECTURING ABOUT GLOBAL WARMING and the resulting Climate Changes, in 1847 !
    .
    “The heat-trapping nature of carbon dioxide & other gases was experimentally demonstrated & *PROVED* in the mid-19th century.”
    ..( these same fundamental experiments are replicated Every year in nearly every college science class 101, around the world !
    …they are put up for critique and every science student takes a shot on the science
    … for decades, no appreciable critique of the science of Global Warming…not in climatology, not in physics, not Earth Science, not physical science, not in Meteorology, etc.)
    .
    "….The line of Solid empirical evidence that humans are causing global warming is as follows
    .
    We're raising CO2 levels and H2O & other gasses.
    Human carbon dioxide emissions & other gasses are calculated from international energy statistics, tabulating coal, brown coal, peat, and crude oil production by nation and year, going back to 1751. CO2 emissions have increased dramatically over the last century, climbing to the rate of 29 billion tonnes of CO2 per year in 2006 (EIA).
    .
    Atmospheric CO2 levels are measured at hundreds of monitoring stations across the globe. Independent measurements are also conducted by airplanes and satellites.
    For periods before 1958, CO2 levels are determined from air bubbles trapped in polar ice cores. In pre-industrial times over the last 10,000 years, CO2 was relatively stable at around 275 to 285 parts per million.
    .
    Over the last 250 years, atmospheric CO2 levels have increased by OVER 100 parts per million. Currently, the amount of CO2 in the atmosphere is increasing by around 15 gigatonnes every year.
    .
    (( Instead of 225-285PPM, as it has been for well over 10,000 years, today we are NOW OVER 410PPM ! ))
    .
    (( What has change which has caused this to occur? ))
    .
    Atmospheric CO2 levels and Cumulative CO2 emissions (CDIAC).
    While atmospheric CO2 levels are usually expressed in parts per million,
    here they are displayed as the amount of CO2 residing in the atmosphere in gigatonnes.
    CO2 emissions includes fossil fuel emissions, cement production and emissions from gas flaring.
    ….
    ( Humans are emitting more than 135 TIMES as much CO2 as ALL of the volcanoes on EARTH, each & every year, COMBINED ! ) <
    .
    CO2 traps heat. <<
    .
    According to radiative physics & decades of laboratory measurements, increased CO2 in the atmosphere is expected to absorb more infrared radiation as it escapes back out to space.

    * In 1970, NASA launched the IRIS satellite measuring infrared spectra.
    * In 1996, the Japanese Space Agency launched the IMG satellite which recorded similar observations.
    * Both sets of data were compared to discern any changes in outgoing I.R. energy radiation over the 26 year period

    SOURCE: (Harries 2001).

    What they found was a drop in outgoing radiation at the wavelength bands that greenhouse gases such as CO2 and methane (CH4) absorb energy.
    The change/reduction in outgoing radiation was consistent with Global Warming theoretical expectations.

    ** Thus the paper found "direct experimental evidence for a significant increase in the Earth's greenhouse effect" and Global Warming.

    ((If Infra Red Energy, does not escape, it is retained in our Earth System as rising temperatures…(( in the Oceans, soil and atmosphere ))

    This result has been confirmed by subsequent Research papers using data from later satellites.
    .
    SOURCE: (Griggs 2004)
    SOURCE: ( Chen 2007 )
    .
    Change in spectrum from 1970 to 1996 due to trace gases.
    'Brightness temperature' indicates equivalent blackbody temperature
    .
    SOURCE: (Harries 2001).
    .
    When greenhouse gases absorb infrared radiation, the energy heats the atmosphere which in turn re-radiates infrared radiation in all directions.
    Much of it makes its way back to the earth's surface.
    .
    Hence we expect to find more infrared radiation heading downwards.
    .
    Surface measurements from 1973 to 2008 find an increasing trend of infrared radiation returning to earth.
    .
    SOURCE: (Wang 2009)
    .
    A regional study over the central Alps found that downward infrared radiation is increasing due to the enhanced greenhouse effect.
    .
    SOURCE: (Philipona 2004)
    .
    Taking this a step further, an analysis of high resolution spectral data allowed scientists to quantitatively attribute the increase in downward radiation to each of several greenhouse gases.
    .
    SOURCE: (Evans 2006)
    .
    The results lead the authors to conclude that "this experimental data should effectively end the argument by skeptics that no experimental evidence exists for the connection between greenhouse gas increases in the atmosphere and global warming."
    .
    Spectrum of the greenhouse radiation measured at the surface.
    Greenhouse effect from water vapor is filtered out, showing the contributions of other greenhouse gases.
    .
    SOURCE: (Evans 2006)
    .
    The planet is accumulating heat
    .
    When there is more energy coming in than escaping back out to space, our climate accumulates heat. The planet's total heat build up can be derived by adding up the heat content from the ocean, atmosphere, land and ice.
    .
    SOURCE: (Murphy 2009)
    .
    Ocean heat content was determined down to 3000 metres deep.
    Atmospheric heat content was calculated from the surface temperature record and heat capacity of the troposphere.
    Land and ice heat content(eg-the energy required to melt ice)were also included.
    .
    Total Earth Heat Content from 1950.
    .
    SOURCE: (Murphy 2009)
    .
    SOURCE: (Ocean data taken from Domingues et al 2008.)
    .
    From 1970 to 2003,
    the planet has been accumulating heat at a rate of 190,260 gigawatts with the vast majority of the energy going into the oceans.
    .
    Considering a typical nuclear power plant has an output of 1 gigawatt, imagine 190,000 nuclear power plants pouring their energy output directly into our oceans.
    .
    What about after 2003?
    A map of of ocean heat from 2003 to 2008 was constructed from ocean heat measurements down to 2000 metres deep .
    .
    SOURCE: (von Schuckmann 2009)
    .
    Globally, the oceans have continued to accumulate heat to the end of 2008 at a rate of 0.77 ± 0.11 Wm?2, consistent with other determinations of the planet's energy imbalance.
    .
    SOURCE: (Hansen 2005)
    SOURCE: (Trenberth 2009).

    The planet continues to accumulate heat.

    1. So we see a direct line of evidence that we're causing global warming. Human CO2 emissions far outstrip the rise in CO2 levels.

    2. The enhanced greenhouse effect is confirmed by satellites and many surface measurements.

    3. The planet's energy imbalance is confirmed by summations of the planet's total heat content and ocean heat measurements…."