Sunday, 29 January 2012

Warming Winters? Meteorologist Paul Douglas' disconnect with reality.

The Minneapolis Star Tribune warns "Warmer winters bring tick-infested springs"
In Minnesota, black-legged ticks have expanded their territory since 2007. More people live in wooded areas where ticks thrive, more mice and other rodents that carry Lyme disease survive warmer winters, and more ticks "hitchhike" on birds and humans.
Then follows some statistics about tick-borne disease (including the nasty "Lyme disease"), and the increasing prevalence of ticks in Minnesota, which I don't dispute. However, at the end we get a (second) quote from meteorologist Paul Douglas:
Winters in Minnesota have grown milder since 1998, Douglas said, with a steep reduction in Arctic air that was common even 20 or 30 years ago. "It's a slow-motion evolution," he said.
That "grown milder since 1998" is precise and checkable so let's do it, starting with NOAA's National Climatic Data Center's data for Minnesota:

NCDC Winter temperatures for Minnesota, 1990-2011

Apart from a downward tick for 2001, average winter temperatures have declined since 1998 (the peak). There's even a statistical downward trend since 1990. Focus in on Minneapolis-St.Paul, 1998-2011:

NCDC Winter Temperatures for Minneapolis-St.Paul 1998-2011

Other cities and towns in Minnesota show a similar trend from 1990, with pronounced cooling since 1998. The NCDC chart shows a downward trend of -0.88°F (-0.49°C) per decade, a whopping 8.8°F (-4.9°C) per century, the Minneapolis-St.Paul data an almost incredible 63.1°F (35°C) per century.

Where has Mr. Douglas been the last two decades, particularly since 1998? More to the point, where does he get his data to support his comment? Who is this Paul Douglas? Wikipedia knows - it seems he's an (ex-) TV weatherman, columnist and blogger. The Wiki page soon reveals something rather relevant :
Douglas regularly writes and speaks about global warming and is critical of those who say that it is not occurring or is not caused by human actions.
I write about global warming and I'm critical of those who say that something is occurring (warmer winters in Minnesota) when it's not. Mr. Douglas thinks Global Warming "deniers" are "immoral" ("Paul Douglas: 'I'm a recovering Republican, and I don't recognize my party any more"). I think those who tell the opposite of the truth are immoral.

As for Mr. Douglas' "steep reduction in Arctic air that was common even 20 or 30 years ago", have a look at "Arctic warming, increasing snow cover and widespread boreal winter cooling":

The most up to date consensus from global climate models predicts warming in the Northern Hemisphere (NH) high latitudes to middle latitudes during boreal winter. However, recent trends in observed NH winter surface temperatures diverge from these projections. For the last two decades, large-scale cooling trends have existed instead across large stretches of eastern North America and northern Eurasia. We argue that this unforeseen trend is probably not due to internal variability alone. Instead, evidence suggests that summer and autumn warming trends are concurrent with increases in high-latitude moisture and an increase in Eurasian snow cover, which dynamically induces large-scale wintertime cooling. Understanding this counterintuitive response to radiative warming of the climate system has the potential for improving climate predictions at seasonal and longer timescales.
"For the last two decades" - I nearly ran out of fingers, but I'm pretty sure Mr. Douglas' 1998 is in there somewhere. Who's the "denier" now?

UPDATE 30th Jan. 2012

The Hufffington Post (such a goldmine of unbiased opinion!) says "On Climate Change, Weathercasters May Be Misguiding Their Viewers"
"If you look at the stats over the past five or six years, the public's belief that global warming is a serious problem, or is even happening, is declining," said Daniel Souweine, co-founder of the nonprofit Citizen Engagement Lab. In fact, nearly 40 percent of Americans are not convinced that the earth is heating up, according to the latest Pew Research Center poll.
"We think that's a result of the fact that they're not getting the right kind of information about what the science says," Souweine told The Huffington Post.
We've proof that one, in particular, isn't giving the "right kind of information", as I've shown graphically.

UPDATE 6th Feb. 2011

I found I'd used a GISS dataset for an entirely different Minneapolis for my original chart (should've spotted  the different lat/lon - silly me!), so to save time sorting THAT out I've substituted the NCDC plot for Minneapolis-St.Paul for the relevant 1998-2011 period.I've altered the text to suit - If anything it reinforces my point.

UPDATE 12th Feb. 2011

On his his Star Tribune blog is a "Send Paul a question" link, so I've done just that, and here it is:
A few weeks ago, you were quoted in a Star Tribune article on ticks in Minnesota:
"Winters in Minnesota have grown milder since 1998, Douglas said, with a steep reduction in Arctic air that was common even 20 or 30 years ago. "It's a slow-motion evolution," he said."
I'm interested in temperature trends, and often use the NCDC "Climate At A Glance" page to check trends for the US. However, using the form for Minnesota to plot winter temps since 1998 shows them to have been declining. I wonder if you could point me to a source that shows the opposite?
I'll let you know if I get a response.

Saturday, 21 January 2012

The Footprint of El Niño - South Pacific Sea level

I've mentioned the intermittent effect of El Niño on South Pacific sea level in several posts. How and why does this part of the ENSO cycle affect sea level?
The primary cause of anomalous ocean conditions is the El Niño/Southern Oscillation (ENSO) in the equatorial Pacific Ocean. Westward winds normally maintain slightly higher water levels in the western Pacific relative to the eastern Pacific. Every three to five years, in a non-periodic pattern, the winds weaken and water levels in the western Pacific drop below normal. The southern equatorial current is weakened and water temperatures in the eastern Pacific rise. This condition is known as El Niño. The opposite condition, known as La Niña, occurs when westward equatorial winds are unusually strong and water levels in the western Pacific become anomalously high. The south equatorial current strengthens, accompanied by below normal water temperatures in the eastern Pacific.
Boiled down, in terms of the effect on sea level, is that levels in the western and south-western Pacific tend to drop, often significantly, during El Niño years, while those in the east tend to rise.

The island of Majuro, in the Marshall Islands reflects this trend particularly well. The opposite La Niña effect, though present, is not so well illustrated. Using data from an earlier gauge maintained by the University of Hawaii, and the later SEAFRAME gauge installed in 1993 by the National Tidal Centre based in Adelaide, Australia, I've been able to reconstruct a history of sea level at Majuro Atoll from 1978 to 2011.

For charts for Majuro and other Pacific Islands, including Tuvalu and Kiribati, see my reference page "South Pacific Sea Level 2011".

Here's a table of El Niño years. Those from 1969 to 2010 are clearly represented on the Majuro chart. The 1982-3 and 1997-8 El Niños were particularly strong events, and I've highlighted them in red

El Niño Years
1902-1903 1905-1906 1911-1912 1914-1915
1918-1919 1923-1924 1925-1926 1930-1931
1932-1933 1939-1940 1941-1942 1951-1952
1953-1954 1957-1958 1965-1966 1969-1970
1972-1973 1976-1977 1982-1983 1986-1987
1991-1992 1994-1995 1997-1998 2002-2003
2006-2007 2009-2010

On the other (eastern) side of the Pacific, continuous long-term records are difficult to find, but that for Monterey, California illustrates the opposite effects quite well, although earlier El Niño years aren't quite so clearly defined.

Not much sign of the 1972-1973 and 1976-1977 El Niños, but the later events are all represented, though to varying degrees. Most of the west and south-west Pacific islands show the "El Niño" effect to differing degrees, but Tuvalu has become the "poster child" of the Global Warming scenario, so it's worthwhile reproducing my reconstruction for that island, covering 1977-2011.

The linear trend shows a value of 0.28 mm/month, which translates to 3.36 mm/year. However, the effect of the El Niños is to pull the trend line down progressively from right to left; it's always below the 13-month running mean (in red), more so on the left. A simple way to eliminate the negative effect of the El Niño "spikes" on the trend is to remove them from the data. However, this is not as easy as it sounds; there's a clear (approximately) annual cycle, illustrated by the sharp upward spikes.  These "king tides" usually occur in late February or early March, occasionally as late as April, and their timing is due to the "lining up" of the tidal effects of both moon and sun. The all-time peak was in February 2006 (very clear on the graph), and despite dire predictions, hasn't yet been surpassed.

An Australian newspaper dispatched a team to Tuvalu in February 2011 to document what was expected to an all-time record "king tide". However, nature being as quirky as ever, organised things so that they'd already "missed the boat" (a metaphor becomes a bad pun!) as the highest tide had already occurred the previous month; indeed the February peak was lower than both January and March peaks. That and the fact that the January peak was no record, produced a "non-event" and no follow-up report was published.

However, I digress - removing the El Niño "spikes" must be done with care if an opposite upward bias is to be avoided. One way round this is to use annual data so the monthly cycle is not a problem, though it effectively removes more data. I'll be following up with a detailed analysis of late-20th century sea level rise at Tuvalu.

Data Sources

Marshall Islands (Majuro): Permanent Service for Mean Sea Level and South Pacific Sea Level and Climate Monitoring Project

Monterey: Permanent Service for Mean Sea Level

Tuvalu (Funafuti): Permanent Service for Mean Sea Level and South Pacific Sea Level and Climate Monitoring Project