The Critical Decade: Climate change science, risks and responses

Our climate is changing. The atmosphere is warming … 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.

And the ocean is warming. Nearly 90% of the excess heat in the climate system is stored in the ocean. Ocean heat content has been increasing steadily since 1955.

More heat is being trapped by the atmosphere. 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.

Human activities are making it warmer. This graph compares climate modeling with actual observations. The purple line shows a model of natural climate variability between 1900 and 2000. The red line shows what happens when the climate models input both natural variability and human caused climate change. The black line shows the actual observations over this period, that is the temperatures actually measured. The observations closely match up with the modeling when natural variability and human caused climate change are put together. Source: IPCC AR4

The changes are affecting our world in many ways. Changes in climate and weather events significantly affect our own health and well-being, our societies and economies, and the natural ecosystems that we not only enjoy in their own right but that also provide us with essential services. In face, climate change is already affecting our lives, often in negative ways, by shifting the basic climatic conditions around which we’ve built industries and infrastructure and by making many extreme weather events worse by increasing their frequency or intensity. Pictured: Grapes: As the life-cycle of wine grapes is predominantly temperature-driven, a changing climate could influence wine grape production and quality across Australian wine regions. Substantial decreases in the climate suitability of current wine-producing regions may be felt by 2050, especially in those regions that have a Mediterranean climate. Water supplies: Australia is the world’s driest inhabited continent. The impacts of climate change on Australia’s water resources are therefore of critical importance for our communities, agriculture, industries and environment. River flows in Australia vary substantially from year to year and decade to decade, exacerbating the multiple conflicting demand on our water supplies. Predicting future changes in rainfall, and therefore water availability than projections of future temperature. Climate models generally predict ongoing drying in the southeast and southwest, with obvious risks to water availability for urban areas and agriculture. However, they predict a range of possible outcomes for northern Australia. To further complicate matters, water availability is not just affected by rainfall. Rising temperatures will increase evaporation and reduce runoff, and any future changes in vegetation cover could also have feedbacks to local rainfall patterns. Climate change will also affect groundwater. Recharge of groundwater systems may decline in the southern, southwestern and central parts of the continent, but increase in the north and some parts of the east. Great Barrier Reef: The Great Barrier Reef (GBR) is the world’s largest continuous reef system (over 2,200 km long, and 375,000 square kilometres in area), and comprises more than 2,900 individual reefs. The GBR is one of the most biologically diverse ecosystems in the world and is a globally-important breeding ground for seabirds and other marine vertebrates such as turtles and whales. The reef is vital to Australia’s tourism and fishing industries, attracting five million visitors to the region in 2008–2009. In 2006–2007, the GBR was estimated to contribute $5.4 billion to the Australian economy, and provided more than 50,000 jobs. The GBR also provides protective services to coastal communities valued at more than $10 billion. Climate change poses multiple, serious threats to the GBR. Sea temperatures only 1–2°C above the average summer maximum (based on the period 1985–93, excluding 1991–92) can cause mass coral bleaching (loss of symbiotic algae) and lower their growth rate. In addition to the impacts of warming waters, corals and other marine organisms are likely to be affected by ocean acidification. Bushfires: Bushfre weather refers to the daily weather conditions that are conducive for the outbreak of a fire – very hot, dry and windy days. Longer-term weather and climate conditions can also affect bushfires through effects on the amount and condition of the fuel load, which is also influenced by a range of non-climate related ecological factors. Climate change is increasing the probability of extreme fire weather by increasing the frequency and intensity of very hot days and hot periods. The projected increase in severity and frequency of climatic conditions that influence bushfire weather, such as higher temperatures and increased aridity, will very likely lead to an increase in frequency of extreme fire danger days in the southeast and southwest of the continent.

We are living in a new climate... This graph shows the statistical link between a changed climate and more extreme temperatures. A small increase in average temperature can have a disproportionately large effect on the number of hot days and record hot days, When the average temperature increases, the temperatures at the hot and cold ends (tails) of the temperature range shift to create a much greater likelihood of very hot weather and a much lower likelihood of very cold weather. The red area at the extreme right shows that record hot weather that occurs only after the shift to the warmer background climate. This means that we are beginning to see weather events that have never been observed since instrumental records were begun, and events that were extremely rare in the previous climate are becoming more common.

With increased frequency and severity of extreme weather events Extreme weather has always occurred. But due to additional greenhouse gases in the atmosphere, the climate system now contains significantly more heat compared to 50 years ago. This means that all extreme weather events are influenced by climate change. The severity and frequency of many extreme weather events are increasing due to climate change. This infographic is from the Climate Commission’s The Critical Decade: Extreme weather. This report profiles six different types of extreme weather, discussing impact, observations, projections and the influence of climate change.

And changing rainfall patterns. Global precipitation patterns are changing, with some notable trends being observed. It is difficult to determine an overall global trend in precipitation because rainfall and snow are highly variable in time and space and there is a lack of data for many regions of the world. In Australia, some pronounced regional rainfall trends have emerged since 1970. In particular, the southwest corner of Western Australia and the far southeast of the continent, along with Tasmania have become drier. Less significant drying trends have also been observed along much of the east coast and in the centre of the continent.

Some of these changes are occurring faster than predicted. The bands of colour on this graph show various projections of Arctic sea-ice loss. The black line shows the observed Arctic sea-ice loss. You can see that ice loss is happening faster than models predicted.

Countries are acting to reduce greenhouse gas emissions… Across the world countries have agreed that deep cuts in greenhouse gas emissions are necessary to prevent global temperatures from rising to levels that will cause significant and irreversible damage. Ninety-eight countries, including the world’s largest economics, the United States of America and China, have now committed to limit their greenhouse gas emissions. There are a range of ways that countries around the world are reducing their greenhouse gas emissions, such as promoting energy efficiency, carbon pricing, carbon storage technologies, improved land management and switching to renewable energy sources. 35 countries have national emissions trading schemes. In addition there are 9 sub-national emissions trading schemes in the United States of America, 2 sub-national schemes in Japan and 1 in China. China is set to begin a further 6 pilot emissions trading schemes from mid-2013. In 2013, 5 new emissions trading schemes commenced including California (USA), Croatia, Kazakhstan, Quebec (Canada) and Shenzhen (China).

And renewables are increasing… In Australia more than 1 million rooftop solar photovoltaic systems were installed by March 2013. This is equivalent to 2.6 million people are using the sun to power their homes.  

But there is an overspend in the carbon budget. For a 75% chance of limiting global temperature rise to 2˚C, we can emit no more than 1,000 billion tonnes of CO₂ FROM 2000 to 2050. That seems like a very large number, but we are already 13 years into that period so we can check on progress against the overall budget. The figures, available for the 2000-2011 period and projected for 2012 are not encouraging. In 2000 fossil fuel emissions were 24.8 billion tonnes of CO₂ and emissions rose to 34.7 billion tonnes in 2011. Another 35.6 billion tonnes is projected for 2012. This brings the total for the 13 year period to 391.0 billion tonnes, nearly 40% of the total allowable budget. That leaves a budget of just over 600 billion tonnes for the next 35-40 years, after which the world economy needs to be completely decarbonised. Under a business-as-usual model, with emissions growing at 2.5% per annum, we are on track to have completely used up the allowable global emissions within the next 16 years, that is by 2028.

This is the critical decade for action. My grandkids? My kids 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 last red 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. Me

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