I wrote this for a different group of people but when I mentioned it in another thread, someone expressed an interest in seeing it here.
It's pretty long for DW but here goes!
Extreme is the new Normal
The headlines have been coming at us every week for a few years now, it seems: Hottest Ever … Record Floods … Highest on Record … Coldest Winter … Record-breaking Drought … and on they go. A vague concern that there are too many of them is certainly justifiable, since extreme events shouldn’t be frequent events: anything that happens often ought, by definition, to be normal. So what’s going on?
Putting it as simply as possible, our idea of ‘normal’ weather is our accumulated experience of weather over thirty or more years - depending on our age! - but weather over thirty or more years is climate, and the climate is changing.
I have been recommending the Australian Bureau of Meteorology’s ‘Climate Trend Maps’ (http://reg.bom.gov.au/cgi-bin/silo/reg/cli_chg/trendmaps.cgi) to people ever since I discovered them. Visiting the site gives you immediate, graphic, images of the changes which have been occurring in our climate since 1900.
The site lets users select variables (rainfall or temperature) and look at the way they have changed over the last hundred years. Click on ‘Annual Rainfall’ for any period since 1900 and a trend jumps out at you: the whole East coast and the extreme South of Western Australia (yes, that is where about 22 of our 22.5 million people live) is getting drier. Looking at different timeframes, you find that the change has been speeding up: the average annual rainfall in Townsville, Brisbane, Sydney and Melbourne has decreased by more than 50 mm per decade over the last forty years. Look at average temperature, and almost the whole map turns red - the only areas that have cooled are little spots in the desert around Kununurra.
Look at North Queensland’s weather on a seasonal basis and you will see that our summers and autumns are drier but winters and spring a little wetter - though not enough to make up for the wet season decrease. Our temperatures are up, just a little, right across the board: annual average and all seasonal averages.
What about the rest of the world? There is a global version of the Trend maps at http://reg.bom.gov.au/cgi-bin/climate/change/global/trendmaps.cgi but it doesn’t show much detail. Let’s look at an overview from one of the world’s biggest climate monitoring agencies instead.
According to NOAA scientists (http://www.noaanews.noaa.gov/stories2011/20110112_globalstats.html), "2010 tied with 2005 as the warmest year of the global surface temperature record, beginning in 1880. This was the 34th consecutive year with global temperatures above the 20th century average." The NOAA summary goes on to say:
NOAA wrote:• 2010 was the wettest year on record, in terms of global average precipitation. As with any year, precipitation patterns were highly variable from region to region.
• The Arctic Sea Ice had a record long growing season, with the annual maximum occurring at the latest date, since records began in 1979. Despite the shorter-than-normal melting season, the Arctic still reached its third smallest annual sea ice minimum on record behind 2007 and 2008.
• A negative Arctic Oscillation (AO) in January and February helped usher in very cold Arctic air to much of the Northern Hemisphere. Record cold and major snowstorms with heavy accumulations occurred across much of eastern North America, Europe and Asia. The February AO index reached -4.266, the largest negative anomaly since records began in 1950.
• From mid-June to mid-August, an unusually strong jet stream shifted northward of western Russia while plunging southward into Pakistan. The jet stream remained locked in place for weeks, bringing an unprecedented two-month heat wave to Russia and contributing to devastating floods in Pakistan at the end of July.
One of the climatologists’ general predictions for what happens when CO2 builds up in the atmosphere is the obvious one, that the Earth as a whole warms up: Global Warming. Accompanying that, however, is that local climate will change by far more than just getting a bit warmer: Climate Change, regionally, will be complex and not all in one direction. As well, weather events will become more extreme. The NOAA summary mentioned a few of last year’s events, but the IPCC (http://www.ipcc.ch/publications_and_data/ar4/syr/en/spms1.html) puts it more generally:
IPCC wrote:Human influences have:
• very likely contributed to sea level rise during the latter half of the 20th century
• likely contributed to changes in wind patterns, affecting extra-tropical storm tracks and temperature patterns
• likely increased temperatures of extreme hot nights, cold nights and cold days
• more likely than not increased risk of heat waves, area affected by drought since the 1970s and frequency of heavy precipitation events.
That’s directly from AR4, published in 2007 and based on research up to about 2005. Worryingly, all the newer research shows that impacts are greater and arriving earlier than predicted.
If the climate is changing, our accumulated experience of weather over our lifetime misleads us.
We think, ‘Fifty years ago when I was a kid it never rained in summer, forty years ago when I was a teenager it never rained in summer, thirty years ago when my kids were little it never rained in summer, so this year’s wet summer is weird and isn’t likely to happen again.’ But climate change means our best guide to next summer’s weather is the 1990s and 2000s weather, not the 1950s and 60s. The same goes for all our other climate-related expectations - fruit tree flowering, bird migrations and the like.
And that’s why we’re seeing all those headlines now. It is impossible to point to a single weather event, whether it’s a flood or a drought, a hailstorm or a cyclone, and say, ‘That is due to global warming,’ but it is certainly possible to point to a whole cluster of extreme events and say, ‘These are due partly to global warming.’
Like it or not, extreme is the new normal.
And if we don’t like it, we know who to blame.