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Instrumental Record

Global warming on Earth

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Translations: (Français)

The Washington Post picked up on the latest update to the 2005 temperature anomaly analysis from NASA GISS. The 2005 Jan-Sep land data (which is adjusted for urban biases) is higher than the previously warmest year (0.76°C compared to the 1998 anomaly of 0.75°C for the same months, and a 0.71°C anomaly for the whole year) , while the land-ocean temperature index (which includes sea surface temperature data) is trailing slightly behind (0.58°C compared to 0.60°C Jan-Sep, 0.56°C for the whole of 1998). The GISS team (of which I am not a part) had predicted that it was likely the 2005 would exceed the 1998 record (when there was a very large El Niño at the beginning of that year) based on the long term trends in surface temperature and the estimated continuing large imbalance in the Earth’s radiation budget.

In 1998 the last three months of the year were relatively cool as the El Niño pattern had faded. For the 2005 global land-ocean index to exceed the annual 1998 record, the mean anomaly needs to stay above 0.51°C for the next three months. Since there was no El Niño this year, and the mean so far is significantly above that, this seems likely. [Read more…] about Global warming on Earth

Hurricanes and Global Warming – Is There a Connection?

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Translations: (Français) (Español)

by Stefan Rahmstorf, Michael Mann, Rasmus Benestad, Gavin Schmidt, and William Connolley

On Monday August 29, Hurricane Katrina ravaged New Orleans, Louisiana and Missisippi, leaving a trail of destruction in her wake. It will be some time until the full toll of this hurricane can be assessed, but the devastating human and environmental impacts are already obvious.

Katrina was the most feared of all meteorological events, a major hurricane making landfall in a highly-populated low-lying region. In the wake of this devastation, many have questioned whether global warming may have contributed to this disaster. Could New Orleans be the first major U.S. city ravaged by human-caused climate change?

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The tropical lapse rate quandary

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Guest commentary by Steve Sherwood

There are four independent instrumental records of sufficient length and potential accuracy to tell us about 20th-century climate change. The two longest ones are of temperature near the Earth’s surface: a vast network of weather stations over land areas, and ship data from the oceans. While land surface observations go back hundreds of years in a few places, data of sufficient coverage for estimating global temperature have been available only since the end of the 19th century. These have shown about a 0.7 C warming over land during the last century, with somewhat less increase indicated over oceans. The land records contain artifacts due to things like urbanization or tree growth around station locations, buildings or air conditioners being installed near stations, etc., but laborious data screening, correction procedures, and a-posteriori tests have convinced nearly all researchers that the reported land warming trend must be largely correct. Qualitative indicators like sea ice coverage, spring thaw dates, and melting permafrost provide strong additional evidence that trends have been positive at middle and high northern latitudes, while glacier retreat suggests warming aloft at lower latitudes.

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Et Tu LT?

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In previous posts we have stressed that discrepancies between models and observations force scientists to re-examine the foundations of both the modelling and the interpretation of the data. So it has been for the apparent discrepancies between the Microwave Sounding Unit (MSU) lower tropospheric temperature records (MSU 2LT), radiosonde records and the climate models that try to simulate the climate of the last few decades. Three papers this week in Science Express, Mears et al, Santer et al (on which I’m a co-author) and Sherwood et al show that the discrepancy has been mostly resolved – in favour of the models.

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Storms and Climate Change

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The Atlantic hurricane season will soon be upon us again , and no doubt many people will recall last year’s devastating Hurricanes that swept across Florida. There was a great deal of press about these storms, as 3 major hurricanes and 5 tropical storms made landfall in the US. According to HurricaneProtection.com, the last time eight different tropical cyclones impacted the United States coastline in a single season was 1916. There were a total of 15 tropical storms and hurricanes, which means that the total number of storms that year was higher than 95% of the previous years of hurricane observations. There was also a record number of Typhoons over Japan in 2004 (10! The previous record was 6 from 1996) . Typhoons are the same as Hurricanes, but have a different name over the Indian ocean and the western Pacific. They are also known as ‘tropical cyclones’. Furthermore, it was the first time that a tropical cyclone had been observed in the south Atlantic (see WMO Climate News, Jan 2005, p. 12)! So, what’s going on?

[Read more…] about Storms and Climate Change

Doubts about the Advent of Spring

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A “consensus view” amongst climate scientists holds that the Northern Hemisphere will be warming this month, as spring is coming. This is thought to be due to the Earth’s orbit around the sun and the inclination of the Earth’s axis, tilting the Northern Hemisphere progressively towards the sun throughout March and April and increasing the amount of solar radiation received at northern latitudes.

In a new novel, State of Euphoria, bestselling author Michael Crikey uncovers major flaws in this theory and warns against false hopes for the arrival of spring.
[Read more…] about Doubts about the Advent of Spring

Worldwide glacier retreat

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Translations: (Français)

One of the most visually compelling examples of recent climate change is the retreat of glaciers in mountain regions. In the U.S. this is perhaps most famously observed in Glacier National Park, where the terminus of glaciers have retreated by several kilometers in the past century, and could be gone before the next century (see e.g. the USGS web site, here, and here). In Europe, where there is abundant historical information (in the form of paintings, photographs, as well as more formal record-keeping), retreat has been virtually monotonic since the mid 19th century (see e.g. images of the glaciers at Chamonix). These changes are extremely well documented, and no serious person questions that they demonstrate long term warming of climate in these regions. New work published in Science (“Extracting a Climate Signal from 169 Glacier Records”) highlights these results, and uses them to make a new estimate of global temperature history since about 1600 A.D., which agrees rather well with previous, independent temperature reconstructions.

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Moberg et al: Highly variable Northern Hemisphere temperatures?

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by William Connolley and Eric Steig

The 10th Feb edition of Nature has a nice paper “Highly variable Northern Hemisphere temperatures reconstructed from low- and high-resolution proxy data” by Anders Moberg, DM. Sonechkin, K Holmgren, NM Datsenko, & W Karlin (doi:10.1038/nature03265). This paper takes a novel approach to the problem of reconstructing past temperatures from paleoclimate proxy data. A key result is a reconstruction showing more century-scale variability in mean Northern Hemisphere temperatures than is shown in previous reconstructions. This result will undoubtedly lead to much discussion and further debate over the validity of previous work. The result, though, does not fundamentally change one of the most discussed aspects of that previous work: temperatures since 1990 still appear to be the warmest in the last 2000 years.

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What If … the “Hockey Stick” Were Wrong?

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Translations: (Français)

The “hockey stick” reconstruction of temperatures of the past millennium has attracted much attention – partly as it was high-lighted in the 2001 IPCC report as one of the important new results since the previous IPCC report of 1995, and partly as it has become the focus of a number of challenges. Discussion about the “hockey stick” is conducted with considerable fervor in the public media, where this curve is often presented as if it were a proof, or even the most important proof, of anthropogenic influence on climate.

As someone who has not worked on the past millennium, I do not want to discuss the merits of the often rather technical challenges (which have been dealt with elsewhere on this site). Rather, I want to discuss the “what if…” question: what if really some serious flaw was discovered in the “hockey stick” curve? What would that mean?

La reconstruction “crosse de hockey” des températures du dernier millénaire a beaucoup attiré l’attention – en partie car elle a été mise en avant dans le rapport IPCC 2001 comme l’un des nouveaux résultats importants depuis le précédent rapport IPCC de 1995, et en partie car elle est devenue le point de mire d’un certain nombre de défis. La discussion sur la “crosse de hockey” est transmise avec une ferveur considérable dans les médias, où cette courbe est souvent présentée comme une preuve ou même la preuve la plus importante de l’influence anthropogénique sur le climat.

En tant que personne n’ayant pas travaillé sur le dernier millénaire, je ne veux pas discuter des mérites des défis techniques (qui sont discutés dans une autre section du site). Je veux plutôt discuter de la question “et si…” : et si de sérieux défauts étaient trouvés dans la courbe “crosse de hockey” ? Qu’est ce que cela signifierait ?

(suite…)

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Anomalous Recent Warmth in Europe

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Translations: (Français)

Guest Contribution by Juerg Luterbacher, University of Bern, Switzerland

While the anomalous nature of recent trends in global average temperature is often highlighted in discussions of climate change, changes at regional scales have potentially greater societal significance. Of particular interest, for example, is the possible relationship between climate change and the incidence of summer heat waves [Meehl, G.A. and C. Tebaldi, Science, 305, 994-997 , 2004] such as those observed in Europe during summer 2003 [see Schaer et al, Nature 427, 332-336 2004; Stott et al, Nature, 432, 610-614­, 2004]. Preliminary analyses of the annual mean surface air temperatures for Europe for 2004 show it be among the few warmest (though not as warm as 1989, 1990, and 1999-2003) since widespread instrumental records have been kept (roughly the past 150 years). 2004 exceeded the reference period (1961-1990) mean temperature by more than 0.8°C. The largest deviations were found over Northern and Eastern Europe. Every single month of 2004 contributed to the overall warmth; February-April, August, October and December were all more than 1°C warmer than the 1961-1990 period. Annual mean European surface air temperatures have increased by around 0.85°C over the last 100 years. The upward trend has accelerated in recent decades, with about 1.2°C of warming taking place over the past 30 years (1975 to 2004). Indeed, the last thirty years likely represent the warmest multidecadal period for Europe in at least the past half millennium [ Luterbacher, J., Dietrich, D., Xoplaki, E., Grosjean, M. and H. Wanner, Science, 303, 1499-1503, 2004], while the last decade (1995-2004) is likely the warmest decade, and summer 2003 the warmest summer. These conclusions are similar to those reached for the entire Northern Hemisphere on the whole.