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While most people now understand that the enhanced greenhouseeffect means a much warmer planet, communicating regional shifts inweather remains a significant challenge. As with most complex science, nuance is everything. But how do youcommunicate complexity and nuance in a world increasingly geared toa 140-character limit? Over the next few days, we ll be looking atthe relationship between climate change and rainfall. Changing the chemistry of the Earth s atmosphere is anuncontrolled experiment. By definition, providing a perfect pictureof the outcome is a difficult task. Nevertheless, our understanding of physics and chemistry hasallowed us to determine with a high degree of confidence the likelyimpact of these changes on the planet as a whole. In the long term but rapidly by geological timescales the Earth will continueto warm. Projected changes to regional weather patterns are much moreuncertain. On the balance of evidence this uncertainty includingthe possibility of abrupt shifts in regional climate actuallyunderscores the dangers of future climate change. However that is not quite the interpretation of some in the broadercommunity, who interpret uncertainty in regional projections asserving to only reduce the risks of climate change. While this is a very strange framework for assessing risk, it hasbeen pervasive enough to confuse efforts to communicate futurechanges, and distorts our assessment of certainty, uncertainty,risk and consequence. Recent heavy rainfall over most parts of Australia, and some of theconversation that has followed, has highlighted many of thesedifficulties. You can t look out your window to gauge future climate change It is clear from the public discourse that there is both a generallack of understanding of the relationship between global warmingand rainfall, as well as confusion around how future rainfallprojections may or may not relate to current and recent rainfallvariability in Australia. It is important to broadly understand that future projections, sayfor 2050, are not dependent on our experience of recent localweather events. This is because climate projections are not anextrapolation of observed data they are based on what willphysically happen if carbon dioxide in the atmosphere keeps rising. People understand this intuitively when it comes to their ownhealth. When a doctor warns a young drinker in their twenties aboutthe risks associated with heavy alcohol consumption over the next40 years, that person tends not to respond that they feel fine nowand hence the doctor is an alarmist. This is because there are very sensible things you can say aboutrisk that are independent of the immediate perceptions of theindividual. This is analogous to climate projections based on fundamentalphysics and chemistry alone. In this context, it should be veryconcerning to all that the climate system is already showing clearevidence of change due to increasing greenhouse gases. That is, thefirst symptoms are already clear . How will rainfall change under global warming? We need to set the scene before tackling this topic. Firstly, climatologically, there is a large difference betweenrainfall and temperature and a large difference in our abilityto provide future projections for rainfall compared withtemperature. To understand this issue, we can use a bit of a thought experiment. If the Earth had a twin, and you added greenhouse gases to itsatmosphere, it would warm up. In fact, any planet that was remotelysimilar to Earth can be expected to behave the same way. But could you use the Earth s twin to understand how globalwarming will change rainfall on our home planet? The answer is yes, but only to a point. As greenhouse gases build up in the atmosphere, a general resultwould quickly become apparent. Our twin planet would have warmeroceans, and a warmer atmosphere holding much more water vapour.Water vapour is itself a greenhouse gas , and is the key positive feedback of the enhanced greenhouseeffect. Across the entire twin planet as a whole, there would be morerainfall. The rainfall is likely to be heavier, and rainfallvariability more extreme. The equatorial regions would most likelybe wetter, and parts of the mid-latitudes drier. The drier regionsof the planet are likely to experience more severe droughtinterspersed by rainfall that is heavier when it does fall. This result is known in the science as an intensification of thehydrological cycle. It has been a consistent feature of climatemodelling over the last 30 years. It is the result that has beenreported in every IPCC report published since 1990. But what does that mean for where I live? While an intensification of the hydrological cycle is a robustconsequence of global warming, rainfall patterns over each regionof the Earth are influenced by much more than just increasinggreenhouse gases. Returning to our twin Earth, we can begin to understand whyprojecting rainfall over individual regions is a much harder taskthan projecting temperature increases. From space, the twin Earth would look almost that same as theplanet we live on. However if you closely inspected the twin, evenbefore you started increasing greenhouse gases, you might well findsome strange things. You might find that its cycle of El Ni o and La Ni a events the ENSO cycle wasn t exactly the same as our Earth. You mayalso find that the location of tropical rainforests and deserts wassimilar, but not exactly the same, from one twin to the other. This shows you how complex rainfall actually is. Weather patternsare a bit like personality; even the Earth s twin will haveslightly different weather and climate. Returning to our analogy of the young alcoholic if he or she hada twin, and they both drank heavily for 40 years, it is likely thatboth would suffer bad health, but not identical symptoms. So while projecting that the Earth will warm up is relativelystraightforward physics, predicting how rainfall will change over asingle region requires a whole different level of scientificprecision. Unfortunately, we don t have a twin planet or a time machine.Fortunately, we do have Earth System Simulators and supercomputers.With these models, we can effectively create not just a twin Earth,but a whole family of Earth-like planets to experiment with. Inthis way, we can get an idea of how rainfall over Australia islikely to change by using many different climate models, andrunning simulations over and over again to examine themechanisms in the models driving the changes. These experimentshave shown us a few things. The models cannot agree on rainfall changes across northernAustralia, with some models suggesting wetter conditions, andothers drier conditions, on average. This actually tells ussomething about the physical predictability of future rainfall inthis part of the world. The models show that a range of different,predominant atmosphere and ocean circulation patterns are equallyplausible for this region as the planet warms. The models are in much better agreement over southern Australia,which is expected to dry, on average, as the planet warms. Thisindicates that something more coherent happens to the atmosphericcirculation in this part of the world, as you heat up the entireclimate system. The models also agree that individual rainfall events will beheavier over most of the continent. This includes over regions thatare expected to dry. Some of that sounds familiar. Isn t this what we have been seeingin Australia? The above rainfall projections are not the simplistic warming=norain scenario that seems pervasive in some public conversations.In particular, there seems to be less of an appreciation in thelocal media that warming is likely to increase rainfall, when averaged across the planet, and increase heavy rainfall events. In this context, the latest research indicates that we are alreadyobserving an increase in very heavy rainfall events around theworld. Closer to home, observed increases in monsoonal rainfall anddecreases in rainfall across southern Australia are consistent witha generalised wetter tropics and drier mid-latitudes scenario. Therecent severe and prolonged drought (and by some measures a recorddrought), ended abruptly by record rainfall, is also consistentwith projections for a warmer world. But before we get ahead of ourselves, it s important to recognisethat climate scientists have stopped short of categorically linkingrecent drought and rainfall to climate change. This is becauserecent events are essentially an intensification of the normalpattern of variability in Australia. When both climate change andnatural variability push in the same direction, we will tend tobreak climate records, but with the amount of global warmingobserved so far it is still difficult to disentangle thecontribution of either when it comes to rainfall extremes. Whether such disentanglement makes much sense is an open question.For climate scientists, it is more than enough to understand thatevery weather system and every ocean current operates in a climatesystem that is now almost 1 degree warmer than at the start of the20th century. That is climate change. Whenever we break records consistent with a warmer world, we aregetting some help from the enhanced greenhouse effect. In thatcontext, some of the characteristics of recent local rainfallextremes are likely to have been influenced, at least partially, bya warming planet. It s not as simple as drought or flood The broader understanding of actual rainfall changes in Australiahas also suffered from simplifications and misinformation in recentyears. While many commentators have simply referred to droughts andfloods, that description lacks nuances that are key to scientificinvestigations. Notably, drought conditions can be realised in many different ways. The most easily understood manifestation of drought is an absenceof meaningful rainfall over long periods. However, in Australia and particularly in those areas where rainfall is not high manyother changes in rainfall can lead to drought. One of the distinguishing features of Australia s climate, incomparison to arid or semi-arid regions elsewhere on the globe, isthe drenching that the entire continent receives on a semi-regularbasis. For some parts of Australia, drought conditions can becaused by a prolonged lack of these very wet years alone, sincethose years are important to the normal hydrological cycle thatecosystems have adapted to. In a water-limited environment, achange in the frequency of future wet years, analogous to a changein the time between drinks, can have a profound impact. Then again, in water-limited environments, drought conditions canalso be caused by a consistent lack of rainfall just in a givenseason, with normal rainfall over the rest of the year. In the recent drought that gripped southeastern Australia from 1995to 2010, a number of different rainfall changes were apparent: An absence of wet years altogether. A systematic reduction in autumn and winter rainfall. These two factors exacerbated one another, leading to prolonged andsevere drought and water shortages. However it is the second factorabove that has scientists most interested. A 10 to 20 per cent loss of autumn and winter rainfall has occurredover both the southwest and southeast corners of the Australiancontinent. This is most significant in the southwest of WesternAustralia, where the changes have occurred since around 1970. Inthe southeast, similar rainfall reductions have been apparent sincethe mid 1990s. We are high quality suppliers, our products such as China French Manicure Nail Stickers , Nail Art Stickers Decals Manufacturer for oversee buyer. To know more, please visits Rhinestone Nail Stickers.
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