What the science tells us about climate change

This content forms part of the issues brief on climate change.

Scientific and experiential evidence of the accelerating risks of climate change trends and impacts is powerful and compelling. Climate change is impacting the world today and, without stronger efforts to curb emissions, more damaging impacts are predicted.

The impact of climate change on Australia today

Climate change is already having damaging and increasing impacts on Australian ecosystems, communities and the economy. Global climate risks are already increasing at an alarming rate.

According to CSIRO and the Bureau of Meteorology, Australia’s climate has warmed in both mean surface air temperature and surrounding sea surface temperature by around 1°C since 1910.

Extreme heat-related events

  • The duration, frequency and intensity of extreme heat events have increased across large parts of Australia.
  • There has been an increase in extreme fire weather, and a longer fire season, across large parts of Australia since the 1970s.

Rainfall, floods and oceans

  • May–July rainfall has reduced by around 19 per cent since 1970 in the south west of Australia.
  • The April-October growing season rainfall in the south east of Australia has declined by around 11 per cent since the mid-1990s.
  • Rainfall has increased across parts of northern Australia since the 1970s.
  • Oceans around Australia are warming and ocean acidity levels have increased.
  • Sea levels have risen around Australia. The rise in mean sea level amplifies the effects of high tides and storm surges.
  • These conclusions are consistent with the findings of the Australia State of the Environment 2016 (SoE) report.

2017 annual climate facts and events

Overview of major Australian climate related trends and events in 2017
Source: Australian Bureau of Meteorology

International trends

The Australian experience of climate change is part of a global picture. The 2014 Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC) concluded that:

Warming of the climate system is unequivocal, and since the 1950s, many of the observed changes are unprecedented over decades to millennia. The atmosphere and ocean have warmed, the amounts of snow and ice have diminished, sea level has risen, and the concentrations of greenhouse gases have increased.

More recently, in 2017, NASA noted that:

The current warming trend is of particular significance because most of it is extremely likely (greater than 95 per cent probability) to be the result of human activity since the mid-20th century and proceeding at a rate that is unprecedented over decades to millennia.

Atmospheric carbon dioxide levels over last 400,000 years
Source: NASA

Global CO2 concentrations in Earth’s atmosphere have risen from 280 parts per million (ppm) in 1780 (the beginning of the industrial revolution) to 316 ppm in 1958 (when first consistently measured at the Mauna Loa Observatory in Hawaii) to over 408 ppm in January 2018.

The last time global CO2 concentrations were above 400 ppm was over 3 million years ago. Global temperatures at that time were 3 to 4°C warmer than they are now (and over 10°C warmer at the poles). Sea levels were over 15 metres higher than they are now.

Earth’s average surface temperature has risen by about 1.1°C since the late 19th Century. Most of this warming has occurred since 1980. 16 of the 17 warmest years on record have occurred since 2001. Five of the warmest years on record have taken place since 2010. 2016 was the warmest year on record. 2017 was the third warmest year on record.

Projections for future risks

Climate modelling scenarios in the most recent (2014) IPCC Fifth Assessment Report indicate a range of likely increases in global surface temperature by 2100 from over 4°C at the highest end (if emissions continue to increase at the rate at which they have over the last 35 years) to 1.5°C at the lowest end (if there is extremely early and rapid action taken to reduce emissions). The 1.5°C outcome would require emission reductions and carbon drawdown at a far more ambitious speed and scale than the current Paris Agreement commitments.

2100 Global warming trends and projections, 1990-2100
Source: Climate Action Tracker

Noting that policies being implemented by many countries are not yet fully consistent with national pledges and bearing in mind the recent withdrawal of the USA from the Paris Agreement, Climate Action Tracker modelling estimates the range of global warming outcomes from successful implementation of current national climate policies in a range from 2.5 to 4.7°C with a median outcome of 3.4°C. A wide range of other leading international climate science and energy research organisations have reached similar conclusions. The most recent analysis of the global carbon budget (the amount of carbon which can be released in order have a reasonable chance of keeping global temperatures below 2°C) provides a different, equally compelling way of understanding the challenges ahead. The 2017 Global Carbon Budget report confirms that annual global emissions are still tracking well above the level needed to achieve the goal of net zero emissions no later than 2040.

While there is widespread agreement that current national climate pledges and policy commitments fall well short of the actions required to achieve the Paris Agreement targets, a number of recent research studies highlight the need to carefully consider the possibility of even higher levels of climate change risk.

One major cause of concern is the increasingly strong evidence that the full extent of global warming is being masked (probably by about 0.9°C) by the presence in the atmosphere of aerosols such as sulphates, nitrates and dust. As necessary and decisive action is taken to reduce these air pollutants (which currently cause over 7 million deaths per year), the rate of global warming is likely to accelerate.

Estimates for global temperature rises with NDCs.
Source: World Resources Institute

Yangyang Xua and Veerabhadran Ramanathan (climate science adviser to the Vatican) also highlight the need to pay close attention to the consequences of low probability/high impact global warming scenarios. In reflecting on their conclusions indicating a 5 per cent chance that global temperatures could rise by as much as 6.5-8.0°C by 2100, we need to carefully consider the confronting question: would we get on a plane or a train which had such a high probability of crashing?

Even if we ignore the fact that 2100 is now well within the lifespan of children already alive – and certainly of our grandchildren – likely global temperature increases for far shorter periods of time also create significant risks. Modelling by the UK Met Office and Climate Action Tracker indicates that global temperatures are likely to exceed 1.5°C in the next decade. The study by Xua and Ramanathan points to a 5 per cent chance of a 3.5-4.0°C temperature increase by 2050.

The landmark study, ‘Trajectories of the Earth System in the Anthropocene’ (Proceedings of the National Academy of Science, 1 August 2018) analysed a wide range of climate tipping points leading to the conclusion that there is a very real chance that the Earth is heading towards a “hothouse climate”. This could lead to average temperatures up to 5°C higher than pre-industrial temperatures and rises in sea level of between 10 and 60 metres.

Importantly this paper also identified an extensive range of urgent actions which need to be taken in order to reduce the likelihood of triggering “hothouse climate” tipping points.

Future climate change

Source: State of the Environment

The Australia State of the Environment 2016 report makes the following predictions in relation to future climate trends for Australia.

  1. Australian temperatures are projected to increase with more extremely hot days and fewer extremely cool days.
  2. An increase in the number of days with weather conducive to fire in southern and eastern Australia.
  3. Extreme rainfall events are likely to increase in intensity by the end of the century across most of Australia.
  4. Decrease of winter and spring rainfall across southern continental Australia, with more time spent in drought.
  5. Fewer tropical cyclones will form in the southern hemisphere than are currently observed, but a higher proportion will be more intense, with ongoing large variability from decade to decade.
  6. Past and ongoing emissions commit us to further sea-level rise around Australia in coming decades, with ongoing sea-level rise.
  7. Oceans around Australia will become warmer and acidification will continue — with significant impacts on marine ecosystems.

The report notes:

“Climate change will result in location-specific vulnerabilities. Australia is predicted to experience increased heatwaves, leading to increased bush fire incidence and health problems (heat stress); longer droughts, extending further geographically; flooding from more intense storm activity; sea level rise, leading to coastal damage; and loss of ecosystems. The 2016 bleaching of the Great Barrier Reef demonstrates how vulnerable Australian ecosystems are to climate change.”

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