1998 not the hottest year on record -- now it's 2005

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Joe Strout - 09 Aug 2007 23:27 GMT

Yes, that was certainly an "oops" moment there, but the upward trend in
even the U.S. data is still pretty clear from the graph:

<http://data.giss.nasa.gov/gistemp/graphs/Fig.D_lrg.gif>

...particularly when you look at the 5-year mean, which helps filter out
the noise. But U.S. temperatures are still a lot more variable than the
global temperature (which makes sense -- air and water currents can
carry heat from one place on the Earth to another, without changing the
total energy of the system). So if you're interested in global warming,
you should be looking at global temperature data, not U.S. data.

That's given by the first plot on
<http://data.giss.nasa.gov/gistemp/graphs/>, the Global Annual Mean
Surface Air Temperature Change. This data is a lot smoother, and the
trend is even easier to see.

So has 1998 really been dethroned as the hottest year on record? Yes;
now it's #2, with a temperature anomoly of 0.57 C. The new champ is
2005, and it's followed closely by 2002, 2003, and 2006. The ten
hottest years on record are all from 1990 or later. The top 19 hottest
years are all after 1980. All but four of the hottest 30 years are
after 1970.

At the other end, the 10 coolest years on record are all before 1920.

So yes, a mistake was made -- and now I'm sure we'll have to endure the
deniers trying to blow it all out of proportion, to cast doubt on the
still-solid evidence of global warming. But as you can see, the climate
is getting steadily hotter worldwide, and no amount of smoke-blowing
from the deniers is going to cool it down.

Best,
- Joe

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kT - 09 Aug 2007 23:42 GMT

> Yes, that was certainly an "oops" moment there

And it's all your's (from RealClimate) :

[Response: McIntyre noticed that there was an odd offset in the GISTEMP
analysis in 2000 which turned out to be related to the transition
between USHCN data to the GHCN data. The offset occurred because the
USHCN corrections (for Time of Observation bias mainly) affect the more
recent values in USHCN but not GHCN (as opposed to only affecting
earlier values). Once notified of the problem, GISS investigated
immediately, found the error, and added an extra step to the analysis to
remove any jump at the transition. This only affected the US
temperatures (reducing the mean by about 0.15 ºC in 2000-2006), but
since the US is such a small part of the world, it doesn’t effect the
global temperatures. Note that this wasn’t a problem with the USHCN data
- rather in how the different data sources are melded. It also had
nothing to do with any micro-site issues. - gavin]

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Pat Flannery - 25 Jul 2008 12:24 GMT

Derek Lyons wrote:

> ...particularly when you look at the 5-year mean, which helps filter out
> the noise. But U.S. temperatures are still a lot more variable than the
> global temperature (which makes sense -- air and water currents can
> carry heat from one place on the Earth to another, without changing the
> total energy of the system). So if you're interested in global warming,
> you should be looking at global temperature data, not U.S. data.

Particularly given two facts about how US temperatures were measured.
1.) This was done in the early years of the 20th century via mercury
thermometers that were considered very accurate if they could get within
three degrees of the actual temperature.
2.) Temperatures were only taken in major cities...with the introduction
of large scale air conditioning, the interior temperature of buildings
dropped far below average in summer, while the heat exchange effect from
the air conditioners raised the ambient air temperature outside of
them. Add to that the effect of indoor heating during winter and it
becomes obvious that any city becomes a major heat well compared to the
ambient temperature of the uninhabited area surrounding it.
But the cause is unimportant when it comes right down to it... the fact
that this summer may see a ice-free sea at the North Pole should give
one pause, and indicate that something odd is going on, and whether it's
man-made or natural will not make any difference whatsoever in regards
to the effect it will have on the planet's climate.
Ocean currents will change, and the particular climates of various parts
of the world will change due to that.
Most animals will probably survive this...they can shift their natural
ranges to new areas where the climate is now similar to where they used
to be.
As to whether farming can survive this is another question. This could
mean planting whole new crops in areas that never grew them before, and
figuring out what the ideal crop for that area is under changed climatic
conditions.
Up here in North Dakota, the overall effect seems to be a positive
one...our winters are far milder, our hottest days in summer are cooler,
and our summer rainfall has increased, although it now tends to come in
large downbursts.
The overall effect is a moderation of our climate, where it doesn't
bottom out at -25 F in winter or get up to 105 F in high summer.
When I was a kid, both of those temperatures could have been expected at
least once in any average year.

Pat

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Space Forum / Space Policy / July 2008

1998 not the hottest year on record -- now it's 2005