Amid all the statistical noise, the evidence says that our carbon emissions are causing a general warming of our planet. [15 April 2008 | Peter Boyer]
Let’s just pretend, for a moment, that there’s no global warming – that it’s just a series of scientific errors or an elaborate hoax. Let’s pretend that the evidence about our run-down planet has been grossly exaggerated, and that we should stop worrying.
Global average temperature for each year from 1881, as determined by NASA’s Goddard Institute (thick red line) and the UK’s Hadley Centre and Climate Research Unit (thin blue line). Both graphs show the temperature relative to the average for the period 1961 to 1990 (shown as 0°C on the graph). This graphic was prepared with advice from Dr John Hunter, Antarctic Climate and Ecosystems CRC, Hobart.
Those who get excited at a good crisis may regret its passing, but most would find it welcome relief. When you hear a scientist say on national radio, as I did recently, that our planet is showing signs of cooling, a big part of you wants her to be right.
Dr Jennifer Marohasy (her doctorate was about biological control agents) is employed by the Institute of Public Affairs, a Melbourne free-market policy organisation.
Dr Marohasy told ABC “Counterpoint” listeners that NASA data showed Earth’s surface temperature was trending down from a high in 1998, revealing serious flaws in greenhouse theory.
If confidence and clear expression were all that counted in the climate debate, Dr Marohasy would be a winner. Listeners unfamiliar with the data she talked about may have felt she was right.
But alas, the evidence says otherwise.
Current and past global average surface temperatures are derived from painstaking assessment of countless readings all over the planet, on land and sea, along with satellite observations, corrected for local aberrations such as the “urban heat island effect”.
The result can’t be exact – the graph shows US and UK calculations that differ slightly – but when it comes to taking the planetary temperature these are the best measures we have.
Over more than two decades, NASA’s Goddard Institute has notified to the world each refinement in its methodology and any adjustments to its calculations – a transparency that has earned its data wide acceptance by climate scientists.
The NASA data says that 1998 was an unusually hot year, but no hotter than last year, 2007, and neither was as hot as the record-breaking 2005. Except for 1998, the hottest seven years since the start of global records in 1881 have been the seven years of this century, from 2001 on.
So where does Dr Marohasy get her idea that 1998 was the pinnacle and that we’ve since stopped warming? Did she really mean to cite the UK’s Hadley Centre and East Anglia Climate Research Unit, an alternative source of global temperature estimates?
The Hadley-CRU data does have 1998 as the hottest year on record, and shows 2006 and 2007 as being cooler than 2005 (the second-hottest year), which seems to support Dr Marohasy’s claim that the trend is at least ambiguous.
But like the NASA data, the UK record also shows each year of this century as being warmer than any previous year except 1998.
And like NASA, the UK record indicates a clear and pronounced warming trend since the mid-1970s.
To understand climate change we need to spot long-term trends, rather than the “noise” of individual years that are much warmer or much colder than years around them.
If only Dr Marohasy were right, we could all feel better about our future. But the evidence is against her. We need solid, sober assessment of the data, not careless, unsupported claims. She has done us no services.