By Simon Torok
Tropical cyclones are an ongoing threat during Australia’s cyclone season, which generally lasts from November to April. On average, the Australian region experiences 13 cyclones a year.
But as the coastlines of Queensland and the Northern Territory are threatened on two simultaneous fronts (Marcia and Lam), we’ve asked our climate scientists what we can expect from tropical cyclones in the future, as Australia’s climate continues to change.
1. Has the frequency of tropical cyclones changed?
Some scientific studies suggest no change and others suggest a decrease in numbers since the 1970s in the frequency and intensity of tropical cyclones in the Australian region.
The Bureau of Meteorology’s satellite record is short and there have been changes in the historical methods of analysis. Combined with the high variability in tropical cyclone numbers, this means it is difficult to draw conclusions regarding changes.
However, it is clear that sea surface temperatures off the northern Australian coast have increased, part of a significant warming of the oceans that has been observed in the past 50 years due to increases in greenhouse gases. Warmer oceans tend to increase the amount of moisture that gets transported from the ocean to the atmosphere, and a warmer atmosphere can hold more moisture and so have greater potential for intense rainfall events.
2. Will the frequency of tropical cyclones change in future?
The underlying warming trend of oceans around the world, which is linked to human-induced climate change, will tend to increase the risk of extreme rainfall events in the short to medium term. Studies in the Australian region point to a potential long-term decrease in the number of tropical cyclones each year in future, on average.
On the other hand, there is a projected increase in their intensity. In other words, we may have fewer cyclones but the ones we do have will be stronger. So there would be a likely increase in the proportion of tropical cyclones in the more intense categories (category 4 or 5). However, confidence in tropical cyclone projections is low.
3. What are the impacts of tropical cyclones?
Today, coastal flooding is caused by storm tides, which occur when low-pressure weather systems, cyclones, or storm winds elevate sea levels to produce a storm surge, which combines with high or king tides to drive sea water onshore. Although rare, extreme flooding events can lead to large loss of life, as was the case in 1899 when 400 people died as a result of a cyclonic storm surge in Bathurst Bay, Queensland.
4. How will impacts of tropical cyclones change in future?
With an increase in cyclone intensity, there is likely to be an increased risk of coastal flooding, especially in low-lying areas exposed to cyclones and storm surges. For example, the area of Cairns’ risk of flooding, by a 1-in-100-year storm surge, is likely to more than double by the middle of this century.
5. How can we adapt to expected changes?
Almost all of our existing coastal buildings and infrastructure were constructed under planning rules that did not factor in the impacts of climate change. However, governments are now taking account of changes in climate and sea level through their planning policies. Just as the building codes and rules for Darwin changed in the wake of Cyclone Tracy, so they should now be re-assessed for each region and locality in Australia to take account of climate change.
You can track both Tropical Cyclone Marcia and Lam using our Emergency Response Intelligence Capability tool (ERIC).
And we also have more information about our latest climate projections here.
Australia is on track for up to 1.7C of warming this century if the world curbs its greenhouse emissions, but under a worst-case scenario could see anything from 2.8C to 5.1C of warming by 2090, according to new climate change projections released by the CSIRO and the Bureau of Meteorology.
The projections are the most comprehensive ever released for Australia. They are similar to those published in 2007, but based on stronger evidence, with more regional detail. These projections have been undertaken primarily to inform the natural resources management sector, although the information will be useful for planning and managing the impacts of climate change in other sectors.
The new report draws on climate model data used by the Intergovernmental Panel on Climate Change (the IPCC). The Fifth IPCC Assessment Report (AR5), released in 2013 and 2014, used a range various greenhouse gas and aerosol scenarios to project future climate change.
Over the past 10 years, carbon dioxide emissions have been tracking the highest IPCC emission scenario (known as RCP8.5). If there is limited international action to reduce emissions, then projections based on the highest scenario may be realised.
However, if emissions are significantly reduced over the coming decades, then intermediate emissions (RCP4.5) might be feasible. Following the low emissions scenario (RCP2.6) would be very challenging given the current trajectory of carbon dioxide emissions.
How does Australia compare?
By late in this century (2090), Australia’s average warming is projected to be 0.6 to 1.7C for a low emission scenario, or 2.8 to 5.1C under a high emission scenario.
The warming under the high scenario is similar to the global average warming of 2.6 to 4.8C under the high emission scenario reported by the IPCC AR5. However, inland areas of Australia will warm faster than coastal areas.
The new projections should be viewed in the context of what has already been observed. Australia has become 0.9C warmer since 1910. Rainfall has increased in northern Australia since the 1970s and decreased in south-east and south-west Australia.
More of Australia’s rain has come from heavy falls and there has been more extreme fire weather in southern and eastern Australia since the 1970s. Sea levels have risen by approximately 20 cm since 1900.
In future, Australia’s average temperature will increase and we will experience more heat extremes and fewer cold extremes. Winter and spring rainfall in southern Australia is projected to decline while changes in other regions are uncertain.
For the rest of Australia, natural climate variability will predominate over rainfall trends caused by increasing greenhouse gases until 2030. By 2090, a winter rainfall decrease is expected in eastern Australia, but a winter rainfall increase is expected in Tasmania.
Historical climate data can be used as an analogue for the future. The analogue could be a location that currently has a climate similar to that expected in another region in the future.
For example, for a warming of 1.5-3.0C and a rainfall decrease of 5-15%, Melbourne’s climate becomes similar to that of Clare in South Australia, Sydney becomes more like Brisbane, and Brisbane becomes more like Bundaberg in inland Queensland.
Extreme rainfall events that lead to flooding are likely to become more intense. The number of tropical cyclones is projected to decrease but they may be more intense and possibly reach further south. Southern and eastern Australia is projected to experience harsher fire weather. The time in drought will increase over southern Australia, with a greater frequency of severe droughts.
A projected increase in evaporation rates will contribute to a reduction in soil moisture across Australia. There will be a decrease in snowfall, an increase in snowmelt, and therefore reduced snow cover.
Sea levels will continue to rise throughout the 21st century and beyond. Oceans around Australia will warm and become more acidic.
What will Australia look like?
Freshwater resources are projected to decline in far south-west and far south-east mainland Australia. Rising sea levels and increasing heavy rainfall are projected to increase erosion and inundation, with consequent damage to many low-lying ecosystems, infrastructure and housing.
Increasing heat waves will increase risks to human health. Rainfall changes and rising temperatures will shift agricultural production zones. Many native species will suffer from reduced habitats and some may face local or even global extinction.
The most vulnerable regions/sectors are coral reefs, increased frequency and intensity of flood damage to infrastructure and settlements, and increasing risks to coastal infrastructure and low-lying ecosystems.
While reductions in global greenhouse gas emissions would increase the chance of slowing climate change, adaptation is also required because some warming and associated climate changes are unavoidable.
By Pep Canadell, CSIRO
Through burning fossil fuels, humans are rapidly driving up levels of carbon dioxide in the atmosphere, which in turn is raising global temperatures.
But not all the CO2 released from burning coal, oil and gas stays in the air. Currently, about 25% of the carbon emissions produced by human activity are absorbed by plants, and another similar amount ends up in the ocean.
To know how much more fossils fuels we can burn while avoiding dangerous levels of climate change, we need to know how these “carbon sinks” might change in the future. A new study led by Dr. Sun and colleagues published today in PNAS shows the land could take up slightly more carbon than we thought.
But it doesn’t change in any significant way how quickly we must decrease carbon emissions to avoid dangerous climate change.
Models overestimate CO2
The new study estimates that over the past 110 years some climate models over-predicted the amount of CO2 that remains in the atmosphere, by about 16%.
Models are not designed to tell us what the atmosphere is doing: that’s what observations are for, and they tell us that CO2 concentrations in the atmosphere are currently over 396 parts per million, or about 118 parts per million over pre-industrial times. These atmospheric observations are in fact the most accurate measurements of the carbon cycle.
But models, which are used to understand the causes of change and explore the future, often don’t match perfectly the observations. In this new study, the authors may have come up with a reason that explains why some models overestimate CO2 in the atmosphere.
Looking to the leaves
Plants absorb carbon dioxide from the air, combine it with water and light, and make carbohydrates — the process known as photosynthesis.
It is well established that as CO2 in the atmosphere increases, the rate of photosynthesis increases. This is known as the CO2 fertilisation effect.
But the new study shows that models may not have quite right the way they simulate photosynthesis. The reasons comes down to how CO2 moves around inside a plant’s leaf.
Models use the CO2 concentration inside a plant’s leaf cells, in the so called sub-stomatal cavity, to drive the sensitivity of photosynthesis to increasing amounts of CO2. But this isn’t quite correct.
The new study shows that CO2 concentrations are actually lower inside a plant’s chloroplasts — the tiny chambers of a plant cell where photosynthesis actually happens. This is because the CO2 has to go through an extra series of membranes to get into the chloroplasts.
This means that photosynthesis takes place at lower CO2 than models assume. But counterintuitively, because photosynthesis is more responsive to increasing levels of CO2 at lower concentrations, plants are removing more CO2 in response to increasing emissions than models show.
Photosynthesis increases as CO2 concentrations increase but only up until a point. At some point more CO2 has no effect on photosynthesis, which stays the same. It becomes saturated.
But if concentrations inside a leaf are lower, this saturation point is delayed, and growth in photosynthesis is higher, which means more CO2 is absorbed by the plant.
The new study shows that when accounting for the issue of CO2 diffusivity in the leaf, the 16% difference between modelled CO2 in the atmosphere and the real observations disappear.
It is a great, neat piece of science, which connects the intricacies of leaf level structure to the functioning of the Earth system. We will need to reexamen they way we model photosynthesis in climate models and whether a better way exists in light of the new findings.
Does this change how much CO2 the land absorbs?
This study suggests that some climate models models under-simulate how much carbon is stored by plants, and in consequence over-simulate how much carbon goes into the atmosphere. The land sink might be a little bigger — although we don’t know yet how much bigger.
If the land sink does a better job, it means that for a given climate stabilisation, we would have to do a little bit less carbon mitigation.
But photosynthesis is a long, long way before a true carbon sink is created, one that actually stores carbon for a long time.
About 50% of all CO2 taken in by photosynthesis goes back to the atmosphere soon after through plant respiration.
Of what remains, more than 90% also returns back to the atmosphere through microbial decomposition in the soils and disturbances such as fire over the following months to years — what stays, is the land sink.
Good news, but not time for complacency
The study is a rare and welcome piece of possible good news, but it needs to be placed in context.
The land sink has very large uncertainties, they have been well quantified, and the reasons are multiple.
Some models suggest that the land will continue to absorb more carbon all throughout this century, some predict it will absorb more carbon up to a point, and some predict that the land will start releasing carbon — becoming a source, not a sink.
The reasons are multiple and include limited information on how the thawing of permafrost will effect large carbon reservoirs, how the lack of nutrients could limit the further expansion of the land sink, and how fire regimes might change under a warmer world.
These uncertainties put together are many times bigger than the possible effect of the leaf CO2 diffusion. The bottom line is that humans continue to be in full control of what’s happening to the climate system over the coming centuries, and what we do with greenhouse emissions will largely determine its trajectory.
Pep Canadell receives funding from the Australian Climate Change Science Program.
By Eamonn Bermingham
Where would we be without the ocean? Swimming, surfing, snorkelling would be tough, not to mention all the yummy food we’d miss. But it has also played a more important role in all of our lives; fulfilling the noblest of causes.
For many years the ocean has been on the front line in the fight to slow down climate change, absorbing around a quarter of the carbon dioxide we produce. The problem is that the scars of this attack are beginning to show.
Ocean acidification is often referred to as the “other CO₂ problem”, and is a chemical response to the dissolving of carbon dioxide into seawater.
The equation is simple: as CO₂ in the atmosphere goes up (and there was a record-breaking increase in 2013), the pH of the ocean falls, with negative impacts on marine biodiversity, ecosystems and society.
But how bad is it?
For the past two years we’ve been working as part of an international team brought together by the United Nations to investigate the impacts of ocean acidification, and our findings have been released today.
The rate of acidification since pre-industrial times and its projected continuation are unparalleled in the last 300 million years, and are likely to have a severe impact on marine species and ecosystems, with flow-on effects to various industries, communities and food security.
We’ve estimated that the loss of tropical coral reef alone – such as the Great Barrier Reef – could end up costing a trillion US dollars a year.
What does the future hold?
Ten years ago, only a handful of researchers were investigating the biological impacts of ocean acidification. Around a thousand published studies later, our understanding of ocean acidification and its consequences has increased tremendously.
Experimental studies show the variability of organisms’ responses to simulated future conditions: some are impacted negatively, some positively, and others are apparently unaffected.
If we are to truly understand the future impacts of ocean acidification, more research is needed to reduce the uncertainties, reduce emissions, and reduce the problem.
Read the full report: “An updated synthesis of the impacts of ocean acidification on marine biodiversity”
The report was compiled by the UN’s Convention on Biological Diversity, an international team of 30 scientists.
As heads of state gather in New York for tomorrow’s United Nations climate summit, a new report on the state of the world’s carbon budget tells them that greenhouse emissions hit a new record last year, and are still growing.
It shows that global emissions from burning fossil fuels and cement production reached a new record of 36 billion tonnes of CO2 in 2013, and are predicted to grow by a further 2.5% in 2014, bringing the total CO2 emissions from all sources to more than 40 billion tonnes. This is about 65% more fossil-fuel emission than in 1990, when international negotiations to reduce emissions to address climate change began.
Meanwhile, deforestation now accounts for just 8% of total emissions, a fraction that has been declining for several decades.
The growth of global emissions since 2009 has been slower than in the prior period of 2000-08. However, projections based on forecast growth in global gross domestic product (GDP) and continuance of improving trends in carbon intensity (emissions per unit of GDP) suggest a continuation of rapid emissions growth over the coming five years.
Global emissions continue to track the most carbon-intensive range among more than a thousand scenarios developed by the Intergovernmental Panel on Climate Change (IPCC). If continued, this situation would lead to global average temperatures between 3.2C and 5.4C above pre-industrial levels by 2100.
There have been other striking changes in emissions profiles since climate negotiations began. In 1990, about two-thirds of CO2 emissions came from developed countries including the United States, Japan, Russia and the European Union (EU) nations. Today, only one-third of world emissions are from these countries; the rest come from the emerging economies and less-developed countries that account for 80% of the global population, suggesting a large potential further emissions growth.
Continuation of current trends over the next five years alone will lead to a new world order on greenhouse gas emissions, with China emitting as much as the United States, Europe and India together.
Country emission profiles
There are several ways to explore countries’ respective contributions to climate change. These include current emissions, per capita emissions, and cumulative emissions since the industrial revolution.
The largest emitters in 2013 were China, the United States, the 28 EU countries (considered as a single bloc), and India. Together, they account for 58% of global emissions and 80% of the emissions growth in 2013 (with the majority the growth coming from China, whereas the EU cut its emissions overall).
Here’s how the major emitters fared in 2013.
Emissions grew at 4.2%, the lowest level since the 2008 global financial crisis, because of weaker economic growth and improvements in the carbon intensity of the economy. Per capita emissions in China (7.2 tonnes of CO2 per person) overtook those in Europe (6.8 tonnes per person).
A large part of China’s high per capita emissions is due to industries that provide services and products to the developed world, not for China’s domestic use. China’s cumulative emissions are still only 11% of the total since pre-industrial times.
Emissions increased by 2.9% because of a rebound in coal consumption, reversing a declining trend in emissions since 2008. Emissions are projected to remain steady until 2019 in the absence of more stringent climate policies, with improvements in the energy and carbon intensity of the economy being offset by growth in GDP and population. The United States remains the biggest contributor of cumulative emissions with 26% of the total.
Emissions fell by 1.8% on the back of a weak economy, although reductions in some countries were offset by a return to coal led by Poland, Germany and Finland. However, the long-term decrease in EU emissions does not factor in the emissions linked to imported goods and services. When accounting for these “consumption” emissions, EU emissions have merely stabilised, rather than decreased.
Emissions grew by 5.1%, driven by robust economic growth and an increase in the carbon intensity of the economy. Per capita emissions were still well below the global average, at 1.9 tonnes of CO2 per person, although India’s total emissions are projected to overtake those in the EU by 2019 (albeit for a population nearly three times as large). Cumulative emissions account for only 3% of the total.
Emissions from fossil fuels declined in 2013, largely driven by a 5% decline of emissions in the electricity sector over the previous year (as shown by the Australian National Greenhouse Gas Accounts). Fossil fuel emissions per person remain high at 14.6 tonnes of CO2.
Is it too late to tame the climate?
Despite this apparently imminent event, economic models can still come up with scenarios in which global warming is kept within 2C by 2100, while both population and per capita wealth continue to grow. Are these models playing tricks on us?
Most models invoke two things that will be crucial to stabilising the climate at safer levels. The first is immediate global action to develop carbon markets, with prices rapidly growing to over US$100 per tonne of CO2.
The second is the deployment of “negative emissions” technologies during the second half of this century, which will be needed to mop up the overshoot of emissions between now and mid-century. This will involve removing CO2 from the atmosphere and storing it in safe places such as saline aquifers.
These technologies are largely unavailable at present. The most likely candidate is the production of bioenergy with carbon capture and storage, a combination of existing technologies with high costs and with environmental and socio-economic implications that are untested at the required scales.
There are no easy pathways to climate stabilization, and certainly no magic bullets. It is still open to us to choose whether we halt our CO2 emissions completely this century – as required for a safe, stable climate – or try instead to adapt to significantly greater impacts of climate change.
What we have no choice about is the fact that the longer emissions continue to grow at rates of 2% per year or more, the harder it will be to tame our climate.
Pep Canadell received support from the Australian Climate Change Science Program.
Michael Raupach has previously received funding from the Australian Climate Change Science Program, but does not do so now.
As World Water Week draws to a close, we want to tell you about a water management project we’re involved with in the developing world.
The Koshi River basin covers some of the poorest parts of China, India and Nepal. The river stretches more than 700km, from China in the north, down through Nepal and across the Himalayas, and finally feeds into the Ganges River. Millions of people live in the region – many of them in flood-prone areas – and rely on the river and the fertile floodplain for their livelihoods.
We’re helping to manage the river better and improve the circumstances of the people living there.
The area is subject to floods, droughts landslides and flows of debris. Erosion also leads to heavy sedimentation, and rivers have been known to change their course.
The effects of climate change aren’t helping, either. Glaciers in the upper reaches of the Basin are melting, bringing water and sediments down to the plains. The people of the Koshi River Basin are in an increasingly vulnerable situation. The impacts of climate change are disturbing water supply and agricultural production. Adding more pressure, the demand for energy and food production is rising.
Raising the stakes even higher, the Koshi Basin also has areas of significant biodiversity, including a UNESCO World Heritage Site.
With funding from the Department of Foreign Affairs and Trade – Australian Aid, we’re working with partners including the International Centre for Integrated Mountain Development, the International Water Management Institute and eWater to develop an integrated modelling framework for the entire basin. We’re helping to develop water balance models that capture the relationship between climate (both rainfall and temperature) and stream-flow (and flood risk) in the Koshi River Basin.
We’re also working on characterising the seasonality and variability of stream flow, and, if possible, the expected trends in stream-flow. We’ll also develop techniques for understanding the likelihood of particular stream-flow estimates.
We aim to use the research and knowledge gained from these projects to allow a regionally coordinated approach to developing and managing the Koshi Basin’s water resources. The people of the area, and the environment, should both benefit.
We rely a lot on climate models. They not only help us understand our present climate, but also allow us to understand possible future conditions and how different regions of our planet are likely to be impacted by climate change.
Having access to this information is vital for the community, government and industries to make informed decisions – sectors like tourism, farming and transportation to name a few.
As useful as these tools are, the reality is that the Earth’s climate system is incredibly complicated. It is affected by an infinite number of variations in the atmosphere, land surface, oceans, ice, and biosphere. How these factors interact with one another, and our socio-economic decisions, further complicates the issue.
In the absence of a twin Earth to use as an experimental control, simulations are the only method we have to understand the future.
Using observed data, advanced algorithms and software systems, scientists have been developing and refining these valuable climate models for years. However in recent times, there has been conjecture about a key aspect of the reliability of these models; whether they are accurately predicting temperature trends?
A new study, published today in Nature Climate Change, shows that yes in fact, they are.
According to the study’s lead author Dr James Risbey, the key to evaluating decadal climate variations is recognising the difference between climate forecasts and climate projections.
He explains that climate forecasts track the detailed evolution of a range of factors, including natural variations like El Niño and La Niña (which put simply is, warm water sloshing around the ocean). This is important because in El Niño and La Niña dominated periods, temperature trends will naturally speed up and slow down.
“Climate projections, on the other hand, capture natural variations, but have no information on their sequence and timing. Since these can impact the climate on a short timescale as much as human activities, their omission from projections creates a mismatch with observed trends. In other words, comparing the two wouldn’t pass the old ‘apples with apples’ test,” he said.
For this latest study, James and his colleagues looked at a range of different climate models that were in phase with natural variability. In doing so, they were able to make meaningful comparisons between model projections and observed trends.
Their analysis showed that in these instances climate models have been very accurate in predicting trends in our climate over the past half century. In other words, climate change models are a lot more than hot air.
Fine out more about our research into climate in our recent report State of the Climate: 2014.
Media Contact: Simon Torok +61 409 844 302 or firstname.lastname@example.org