There is no doubt that the climate is changing. Over the last 50 years air temperature has been increasing and every decade has been warmer than the decade before. In fact, 2000-2009 was the hottest decade since records began. From about 1970, the long-term temperature trend has been strongly upward, consistent with the increase in the rate of greenhouse gas emissions since the mid-20th century. The rise in global average temperature over the past century has been about 0.8˚C.
Nearly 90% of the excess heat in the climate system is stored in the ocean. Ocean heat content has been increasing steadily since 1955.
The greenhouse effect is an important and natural process that keeps the temperature on Earth suitable for life. The ‘enhanced greenhouse effect’ is what we refer to when talking about the causes of climate change. Incoming light and higher energy radiation from the sun penetrate through the Earth’s atmosphere, with some of this radiation reflected back out to space by clouds and bright surfaces such as the white polar ice sheets. But much of this incoming energy is absorbed by land and water at the Earth’s surface.To maintain its energy balance, the Earth emits energy back into space equivalent to the energy which is absorbed. But this energy is emitted in a different form to how it arrived from the sun, as heat not light. This is where greenhouse gases come in. Although they are mostly transparent to the incoming solar radiation they trap some of the outgoing heat, keeping the Earth’s atmosphere, and hence the surface also, warmer than they would otherwise be.This natural greenhouse effect is very important. Without it the Earth’s surface would be over 30 degrees Celsius colder than it is today.Human activities, particularly the burning of fossil fuels, are adding more greenhouse gases to the atmosphere. This is increasing or enhancing the greenhouse effect, trapping more heat in the atmosphere and causing global temperatures to rise.You can think about the Earth’s temperature like a doona: the more feathers in a doona, the more heat is trapped. The more greenhouse gases in our atmosphere, the more heat is trapped, which makes the Earth warmer.
The summer of 2012/13 was remarkable for the number of heat records that were broken. There were seven consecutive days over 39 degrees, averaged over the entire country, smashing previous records. In 102 years of records in Australia, there have only been 21 days over 39 degrees and eight of those occurred last summer.
Australia has a long history of fire and already faces the regular risk of serious and extreme fire danger conditions. Over the past decade large and uncontrollable fires destroyed 500 house in Canberra in 2003, bushfires in Victoria in 2009 took 173 lives and destroyed over 2,000 houses and in 2013 large fires in Tasmania destroyed nearly 200 properties and forced the evacuation of hundreds of people from the Tasman Peninsula. Climate change can affect bushfire conditions by increasing the probability of extreme fire weather days.
Many parts of Australia, including southern New South Wales, Victoria, Tasmania and parts of South Australia have seen an increase in extreme fire weather over the last 30 years. The projections for the future indicate a significant increase in dangerous fire weather for southeast Australia.
A high sea-level event is a coastal flooding or inundation event caused by wind-driven waves or a storm surge, generally exacerbated by a high tide.A storm surge is a rise above the normal sea level resulting from strong onshore winds and/or reduced atmospheric pressure. Storm surges accompany tropical cyclones as they make landfall but can also be formed by intense low-pressure systems in non-tropical areas, such as ‘East Coast Lows’ in the Tasman Sea. Sea-level rise increases the base sea level and thus exacerbates the effects of a storm surge.
Sea level is projected to continue to rise into the 21st century, multiplying the risk of coastal flooding. Even a sea-level rise of 0.5 m could lead to large increases in the frequency of flooding, typically by several hundred times compared to the baseline.
The physical connection between a warming climate and more rainfall is well understood, especially for rainfall that comes from the ocean. Higher temperatures in the surface ocean waters lead to more evaporation and because the atmosphere is warmer, it can hold more water vapour. This leads to a higher water vapour content in the atmosphere. As a result, higher precipitation increases in many locations, with a higher proportion of the precipitation coming as heavy falls.
Extreme and extend rainfall over large areas of Queensland led to record-breaking and very damaging flooding in Queensland in December 2010 and January 2011. December 2010 was Queensland’s wettest December on record. The floods also broke river height records at over 100 observation stations. Thirty three people died with three remaining missing, and 78% of the state (an area larger than France and Germany combined) was declared a disaster zone. The floods created major risks, including contamination of drinking water and food and difficulties in accessing health services and treatments.Approximately 2.5 million people were affected and 29,000 homes and businesses experienced some form of flooding. The economic cost of the flooding was estimated to be in excess of $5 billion.Major damage occurred to infrastructure, including thousands of kilometres of road and rail, as well as to electricity generation and distribution and to other essential infrastructure. Over 3,000km of Queensland Rail track were affected, much of the electrical infrastructure in the Lockyer Valley was destroyed, and around 300,000 homes and businesses lost power in Brisbane and Ipswich at some stage during the floods.
This graph depicts two possible futures. The black wiggly line shows the temperature that we’ve already had. The blue-bar section shows the future temperatures if we limit greenhouse gas emissions to achieve agreed targets. The red section shows the projected future if we allow greenhouse gases to continue to accelerate unabated. The red lines indicated the projected life span of Climate Commissioner, Professor Lesley Hughes, and that of her children and future grandchildren.The first red bar titled ‘me’ indicates the average warming experienced by Professor Hughes over her lifetime. The second red bar, titled ‘my kids’ indicates the average warming that Professor Hughes’ children are expected to experience. The third red line. Titled ‘my grandkids’ indicates the average warming Professor Hughes’ future grandchildren are expected to experience. This lastred bar is placed at around 4.5˚C higher than pre-industrial temperatures. This is a world that would be vastly different to the one in which we live in now. To put this in perspective, if we get to 1.5˚C above pre-industrial levels would be warmer temperatures than ever experienced by humans. A 5˚C difference is the difference between an ice age and now.This is the critical decade to take action to reduce greenhouse gas emissions so that we achieve a future within the blue lines, and a world in which we can live.
The Critical Decade 2013: Influence of climate change on extreme weather events
The Critical Decade 2013
The influence of climate change on
extreme weather events
Our climate is changing.
The atmosphere is warming …
Climate change is influencing extreme
weather events …
Including heatwaves …
Source: Bureau of Meteorology
123 climate records broken during
Australia’s Angry Summer
• Severe heatwave across 70% of Australia in late
December 2012 and early January 2013. Temperature
records set in every state and territory.
• Hottest ever area-averaged Australian maximum
temperature on 7 January 2013: 40.30˚C.
• January 2013 - hottest month on record for Australia.
• All-time high maximum temperatures at 44 weather
• Average daily maximum temperature for whole of
Australia was over 39˚C for seven consecutive days
Source: Vic DHS 2009
The Melbourne 2009 heatwave caused more
deaths than the Black Saturday bushfires.
Source: IPCC AR4
Even a small increase in average temperature
can cause a big change in hot weather.
• Climate change exacerbates bushfire conditions by
increasing the frequency of very hot days.
• Between 1973 and 2010 the Forest Fire Danger Index
increased significantly at 16 of 38 weather stations
across Australia, mostly in the southeast. None of the
stations showed a significant decrease.
• Projected increases in hot days across Australia, and
in dry conditions in the southwest and southeast, will
very likely lead to more days with extreme fire danger
in those regions.
Warming influences bushfire conditions.
Sea level is rising…
Western Australia –
Torres Strait Islands
Heavy rainfall and flooding affects
communities and infrastructure.
• December 2010 was Queensland’s wettest
December on record
• Floods broke river height records at over 100
• 78% of the state was declared a disaster zone
• Economic cost estimated to be in excess of $5 billion
• 300,000 homes and businesses lost power in
Brisbane and Ipswich
For example, the Queensland 2010/11
This is the critical decade for action.
Prof Lesley Hughes