GrahamY

If the realclimate article wasn't clear enough then try this report on Arctic climate over the past century: ( http://www.nersc.no/AICSEX/rep218.pdf ). The authors show Arctic warming of the 1930s confined to a small area and probably due to natural variability, whereas warming at the end of the century was widespread and unlikely to be due to natural variability. To give an analogy, it is like arguing that average sea levels are lower today because they were higher at one location twenty years ago. To show trends above local and short term variability requires widespread measurements over a long time.

As for doubting that Tuvalu an Kiribati are threatened by rising sea levels, you might wonder why the doubts are not more vigorously pursued by sceptics. Sea encroachment in Tuvalu is made worse by population growth, but this fact is largely ignored by the sceptics: Showing that population growth can be environmentally destructive hardly serves the interests of growth proponents. The sea level data however is clear ( http://www.bom.gov.au/fwo/IDO60101/IDO60101.200608.pdf ), the trend since the early 1990s being an average rise of about 6 mm per year. As an aside, if you look at the sea level graph on page 25 of the report you will note that the rising trend is small compared to the amplitude of the natural oscillations, leaving the data ripe for cherry picking sceptics, though the longer a trend continues the harder it becomes to find cherries.

Further to Johnj's comment, here is a Scientific American article which supports Mann's study and claims that the conclusions were the same when Wegman's criticisms were addressed ( http://www.sciam.com/article.cfm?chanID=sa006&articleID=000D5C47-C124-1509-805C83414B7FFDB0 ). The article also commented that the National Research Council of the National Academy of Sciences conducted an independent review and revision of Mann's study and came to the same conclusions.

Unfortunately, scepticism of global warming seems to be mutating to a politically driven process of public deception by recycling debunked arguments and iron curtain style attempts to suppress the freedom of scientists to report their findings.

I can't believe there is even a discussion here on whether global warming is "real" or not. Denialists are so dumb they don't even know why they are denialists. If they were all taking money from ExonMobil, I'd have more respect for them. Instead, they function from a sedimented, wholly-ideological refusal to look critically upon the way we live our lives and cost of the enormous expansion of human activity upon the planet. Don't think. Don't be skeptical. Just go shopping.

Sorry it took me so long to get here, but I'm not a regular and hence had to sign up. Also I work outside during the day (in the weather!)

First, thanks to ChristinaMac for picking up the mistake in the text. I put it down to ageing synapses, but that doesn't excuse the two other people who read it prior to posting. It's fixed now.

Generally I am happier for people with a science background to deal with the doubters and denialists. Thankfully there are some here. Actually John Quiggin declared the debate over on 4 January this year (http://johnquiggin.com/index.php/archives/2006/01/04/the-end-of-the-global-warming-debate/) and I always believe what Quiggin says! I feel we spend a lot of time and energy on arguing the toss when there are urgent things to discuss.

I posted some additional comments (I was up against the word limit) over at my usual patch at Larvatus Prodeo (http://larvatusprodeo.net/2006/10/05/facing-the-knowns-and-unknowns-of-climate-change/). You're welcome to comment there.

I'll have to leave it there tonight. I hope to come back tomorrow night, if they don't close these things off.

The globe is warming by 0.17 degrees Celsius/decade. I have heard James Hansen talk about a global temperature increase of 2 degree Celsius by 2050. Utterly impossible – the measured trend of temperature increase over the past twenty five years simply cannot support such a conjecture. Do the math yourself.

Sea level has risen by 2-3mm per year for the past 150 years and shows no signs of accelerating. Again, do the math yourself. Multiply by 100 – double it for uncertainty – and you get 600mm or 2 ft sea level rise over this century. This is pretty much consistent with the
IPCC.

James Hansen attributes some of the recent global warming to solar influences. Another influence is the Pacific Decadal Oscillation (PDO) – multi decadal patterns of persistent El Nino (warm phase) or La Nina (cool phase) conditions.

It is true that Arctic temperatures in the 30’s and 40’s were as high as today. Real Climate dismisses this by saying that a trend cannot be determined on the basis of the limited data set. Real Climate ignores the tree ring and ice core data tracing the cycle back for 400 years.

Al Gore is a liar. He says that 2005 was the warmest year on record. The highest temperature on record is 1998 according to NASA sources. The simple truth is that the global temperature trend is declining as would reasonably be anticipated in a cool phase of the PDO.

I am a scientist – I argue that the measured scientific data should be at the centre of the scientific debate rather than marginalised by imaginative climate scenarios.

A cool phase of the PDO brings with it a persistent La Nina pattern over several decades. This means that Australia will have warmer winters, many more storms and cyclones and much more summer rainfall over the next few decades. In the context of our horrendous and long lasting drought – this is a brave but testable hypothesis.

Sorry Indigo, but I'm confused.

I scratched around on the NASA website, and only found one reference to 1998 being the hottest year on record:
http://eospso.gsfc.nasa.gov/eos_observ/1_2_99/p38.html
This post was made in 1999, so obviously they did not have temperature data for 6 years in the future. It does say however, that the 90's were the hottest decade on record.

I did however find a NASA webpage that labeled 2005 as:
"The year 2005 was likely the hottest year in more than a century. According to a study by the NASA Goddard Institute for Space Studies (GISS) examining temperatures around the world, 2005 was either the warmest or tied for the warmest ever recorded. According to the GISS team, global warming is now 0.6°C (about 1°F) over the past 30 years, and 0.8°C (about 1.4°F) over the past 100 years."

http://visibleearth.nasa.gov/view_rec.php?id=17438

I'm sorry, but your claim that NASA has rebuked Al Gore seems spurious. Perhaps I'm missing something here? Perhaps, as a scientist, you should know to quote sources when providing raw data (or citing it). Could you possibly source your claims please?

I will ask similar question of you on your claims about the arctic temperatures. Such claims seem at odds with the direct measurements of:
http://arctic.atmos.uiuc.edu/

Regarding your claims about sea level change. I'm an engineer and a mathematician. My friend and I sat down and did some maths, and attempted to estimate the sea level rise if the Greenland (2.85 million km3) ice cap melted using data off wikipedia. We used a thin shell approximation. Our answer was in the ball park of the accepted answer of 7.2m sea level rise. I fail to see how your criticsim of a constant sea level rise would hold, since the loss of the the Greenland ice cap is accelerating. In 1996, Greenland lost about 96km3 , in 2006, this was estimated at 239km3. See (once again from NASA)
http://www.jpl.nasa.gov/news/news-print.cfm?release=2006-023

Sorry to doubt the claims of a fellow scientist, but they don't seem to stack up, and you haven't provided imperical evidence

I did a quick check via google and came to the same conclusion ChrisC. According to NASA http://www.nasa.gov/vision/earth/environment/2005_warmest.html the hottest years since the 1890s are (in order) 2005, 1998, 2002, 2003 and 2004. I'm not a scientist, but that looks like a warming trend to me....

I'm a little dubious about the Greenland ice cap. According to this article http://www.newscientist.com/article.ns?id=dn4864 it could take 1000 years for the ice cap to melt, but once started the process may be irreversible. Confirms a rise of 7 metres, but gives us plenty of warning on a sea-level rise.