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Research: Volcanic Aerosols Largely Responsible for Recent Warming Slowdown

10:20 am in Uncategorized by WeatherDem

Climate change skeptics used the recent slowdown in observed surface warming to claim that 20th century warming was temporary and that the Earth would return to lower average annual temperatures.  They offered up many potential explanations for the slowdown, none of which make physical sense.  The Sun’s 11-year cycle (often used to explain away warming), a primary argument brought forth, is not the reason: this cycle’s solar maximum is near at hand, yet warming has slowed down recently.

Recently accepted research points to a viable physical explanation.  In addition to oceanic transport of heat to the deep ocean and recent La Nina events, sulfuric emissions from small and mid-sized volcanoes entered the lower stratosphere and reflected more incoming solar radiation than normal.  This research separated the effect of natural sulfur emissions from anthropogenic emissions, using a model, to determine the former had a much larger influence than thought.  Aerosol optical depth (AOD) is a calculated metric used to represent how opaque or transparent the atmosphere is to different radiation wavelengths.  The layer between 20 and 30 km increased 4-10% per year since 2000, which is a significant change from normal conditions – significant enough to have effects on Earth’s climate.

Here is one of the paper’s graphical results:


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Figure 1. Observed and modeled time series of stratospheric AOD from three latitude bands.  Satellite observations are represented by the black line.  Base-line model runs are in green. Model runs with the increase in anthropogenic emissions from China and India are in blue. The dashed blue line depicts a model run with 10x the actual increase in anthropogenic emissions. The model run with volcanic emissions is in red. The black diamonds and initials along the bottom of the plot represent the volcanic eruptions that were included in the model run. (Source: Neely paper; subs. req’d.)

As the caption says, satellite measurements are denoted by the thick black curve.  Note the large increase in AOD (higher opacity) over the tropics in the mid-2000s (b) and the large AOD increase over the northern mid-latitudes in the late-2000s (a).  While not a perfect fit to the observations, the model run with volcanic eruptions (red curve) does the best job of explaining the origin of the SO2.  Individual eruptions are indicated by black diamonds on the bottom of each sub-plot.  The effects of volcanic eruptions on climate are, in a general sense, well-known.  Injections of SO2 into the stratosphere reflects sunlight, which reduces the amount of energy entering the Earth’s climate system.  The difference between one large-scale eruption (e.g. Pinatubo in 1991) or many mid-sized eruptions in a short time-period (see above) is not large as far as the climate is concerned.

This could be good news as far as the climate is concerned, at least in the shorth-term.  If incoming energy were reflected back into space instead of being stored in the system, we can physically explain the observed temperature trend slowdown (see Figure 2) and treat the slowdown as real instead of waiting for that energy to transfer from the oceans to the atmosphere, for example.

There is also bad news however.  From the study (emphasis mine):

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NASA & NOAA: 2012 Was In Top-10 Warmest Years For Globe On Record

10:12 am in Uncategorized by WeatherDem

According to data released by NASA and NOAA this week, 2012 was the 9th or 10th warmest year (respectively) globally on record.  NASA’s analysis produced the 9th warmest year in its dataset; NOAA recorded the 10th warmest year in its dataset.  The two agencies have slightly different analysis techniques, which in this case resulted in not only different temperature anomaly values but somewhat different rankings as well.

The details:

2012’s global average temperature was +0.56°C (1°F) warmer than the 1951-1980 base period average (1951-1980), according to NASA, as the following graphic shows.  The warmest regions on Earth (by anomaly) were the Arctic and central North America.  The fall months have a +0.68°C temperature anomaly, which was the highest three-month anomaly in 2012 due to the absence of La Niña.  In contrast, Dec-Jan-Feb produced the lowest temperature anomaly of the year because of the preceding La Niña, which was moderate in strength.  And the latest 12-month period (Nov 2011 – Oct 2012) had a +0.53°C temperature anomaly.  This anomaly is likely to grow larger in the first part of 2013 as the early months of 2012 (influenced by La Niña) slide off.  The time series graph in the lower-right quadrant shows NASA’s 12-month running mean temperature index.  The recent downturn (2010 to 2012) shows the effect of the latest La Niña event (see below for more) that ended in early 2012.  During the summer of 2012, ENSO conditions returned to a neutral state.  Therefore, the temperature trace (12-mo running mean) should track upward again as we proceed through 2013.

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Figure 1. Global mean surface temperature anomaly maps and 12-month running mean time series through December 2012 from NASA.

According to NOAA, 2012’s global average temperatures were 0.57°C (1.03°F) above the 20th century mean of 13.9°C (57.0°F).  NOAA’s global temperature anomaly map for 2012 (duplicated below) reinforces the message: high latitudes continue to warm at a faster rate than the mid- or low-latitudes.

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Figure 2. Global temperature anomaly map for 2012 from NOAA.

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State of Polar Sea Ice – January 2013: Arctic Below and Antarctic Above Normal

8:25 am in Uncategorized by WeatherDem

Global polar sea ice area in early January 2013 remains below climatological normal conditions (1979-2009), but has improved in the past month.  Antarctic sea ice loss is occurring at a climatological normal rate.  Arctic sea ice gain is slightly more rapid than normal, but we should expect this given the record low extent that occurred in September 2012.  Polar sea ice recovered from an extensive deficit of -2.5 million sq. km. area late last year to a -500,000 sq. km. anomaly within the last week.

In March-April 2012, global sea ice area was above normal, but sea ice area anomaly quickly turned negative and then spent an unprecedented length of time near the -2 million sq. km. deficit in the modern era in 2012.  Generally poor environmental conditions (warm surface temperatures and certain wind patterns) established and maintained this condition, predominantly across the Arctic last year.  For the third time in modern history, the minimum global sea ice area fell below 17.5 million sq. km. and for the fourth time in modern history, the anomalous global sea ice area fell below -2 million sq. km.  This is a significant development given that Antarctic sea ice area has been slightly above average during the past few years.  This means that the global anomaly is almost entirely due to worsening Arctic ice conditions.

The rapid ice melt and record-setting area and extent values that occurred in 2012 are the top weather/climate story for 2012, in my opinion.  I think we have clearly seen a switch to new conditions in the Arctic.  Whether these events will occur in similar magnitude or are merely transitory as the Arctic continues to move to a new stable state that the climate will not achieve for years or decades remains to be seen.  The problem is we don’t know all of the ramifications of moving toward or achieving that new state.  Additionally, I don’t think we want to know.

Arctic Ice

According to the NSIDC, weather conditions once again caused less freezing to occur on the Atlantic side of the Arctic Ocean and more freezing on the Pacific side.  Similar conditions occurred during the past six years.  Sea ice creation during December measured 2.33 million sq. km.  Despite this rather rapid growth, December′s extent remained far below average for the month.  Instead of measuring near 13.36 million sq. km., December 2012′s extent was only 12.2 million sq. km., a 1.16 million sq. km. difference!  The Barents and Kara Seas remained ice-free, which is a very unusual condition for them in December.  Recent ice growth in the Seas has slightly alleviated this state, but this is happening very late in the season.  The Bering Sea, which saw ice extent growth due to anomalous northerly winds in 2011-2012, saw similar conditions in December 2012.  This has caused anomalously high ice extent in the Bering Sea.  Temperatures over the Barents and Kara Seas were 5-9°F above average while temperatures over Alaska were 4-13°F below average.  The reason for this is another negative phase of the Arctic Oscillation, which allows cold Arctic air to move southward.  This allows warm sub-arctic air to move north.

In terms of longer, climatological trends, Arctic sea ice extent in December has decreased by 3.5% per decade.  This rate is closest to zero in the spring months and furthest from zero in late summer/early fall months.  Note that this rate also uses 1979-2000 as the climatological normal.  There is no reason to expect this rate to change significantly (more or less negative) any time soon, but increasingly negative rates are likely in the foreseeable future.  Additional low ice seasons will continue.  Some years will see less decline than other years (like this past year) – but the multi-decadal trend is clear: negative.  The specific value for any given month during any given year is, of course, influenced by local and temporary weather conditions.  But it has become clearer every year that humans have established a new climatological normal in the Arctic with respect to sea ice.  This new normal will continue to have far-reaching implications on the weather in the mid-latitudes, where most people live.

Arctic Pictures and Graphs

The following graphic is a satellite representation of Arctic ice as of September 17, 2012 (yes, it’s been that long since I’ve written a Polar post):

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Figure 1UIUC Polar Research Group‘s Northern Hemispheric ice concentration from 20120917.

Here is the similar image from January 9, 2013:
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2012: Hottest Year On Record For United States

3:13 pm in Uncategorized by WeatherDem

After a brief hiatus (10 graduate school credits & TA-ing leaves no time for blogging), I’m back posting on FDL.  I expect to post much more regularly in 2013 as school activities ramp down.  More of my writing will also include a policy angle.  I want to do more to bridge the science and policy worlds in my blogging as well as in my future career.

It’s official: 2012 was indeed the hottest year in 100+ years of record keeping for the contiguous U.S. (lower 48 states).  The record-breaking heat in March certainly set the table for the record and the heat just kept coming through the summer.  The previous record holder is very noteworthy.  2012 broke 1998′s record by more than 1°F!  Does that sound small?  Let’s put in perspective: that’s the average temperature for thousands of weather stations across a country over 3,000,000 sq. mi. in area for an entire year.  Previously to 2012, temperature records were broken by tenths of a degree or so.  Additionally, 1998 was the year that a high magnitude El Niño occurred.  This El Niño event caused global temperatures to spike to then-record values.  The latest La Niña event, by contrast, wrapped up during 2012.  La Niñas typically keep global temperatures cooler than they otherwise would be.  So this new record is truly astounding!

The official national annual mean temperature: 55.3°F, which was 3.3°F above the 20th century mean value of 52°F.

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Figure 1 – NOAA Graph showing year-to-date average US temperatures from 1895-2012.

This first graph shows that January and February started out warmer than usual (top-5), but it was March that separated 2012 from any other year on record.  The heat of July also caused the year-to-date average temperature to further separate 2012 from other years.  Note the separation between 2012 and the previous five-warmest years on record from March through December.  Note further that four of the six warmest years on record occurred since 1999.  Only 1921 and 1934 made the top-five before 2012 and now 1921 will drop off that list.

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Figure 2 – Contiguous US map showing state-based ranks of 2012 average temperature.

Nineteen states set all-time annual average temperature records.  This makes sense since dozens of individual stations set all-time monthly and annual temperature records.  Another nine states witnessed their 2nd warmest year on record.  Nine more states had top-five warmest years.  Only one state (Washington) wasn’t classified as “Much Above Normal” for the entire year.  The 2012 heat wave was extensive in space and severe in magnitude.

Usually, dryness tends to accompany La Niña events for the western and central US.  This condition was present again in 2012, as the next figure shows:

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State of the Poles – Mid-September 2012: Record Low Arctic Ice Extent; Antarctic Ice Above Climatological Normal

7:29 am in Uncategorized by WeatherDem

Judging by recent search terms used to get to this blog and the relative recent peak in traffic, readers have been searching for this post.  I wanted to wait a little longer into the month so that I could capture the expected Arctic minimum, which officially occurred on the 16th of September.  The NSIDC announced this date, after which I started gathering the plots that are found below.  This post will be longer than it usually is because this year’s minimum shattered the record minimum set in 2007, which shattered the previous record set in 2005.  Most of the post is made up of figures, so I encourage readers to at least view them to get a good picture of today’s conditions.  I’m purposefully framing things this way to relay the truly stunning situation the Arctic is in today.  2012 is additional proof the Arctic cryosphere is searching for a new stable point, but hasn’t found it yet.  That does not bode well for the rest of the globe.  With that, let’s begin.

The state of global polar sea ice area in mid-September 2012 remains significantly below climatological normal conditions (1979-2009).  Arctic sea ice loss is solely responsible for this condition.  In fact, if Antarctic sea ice were closer to its normal value, the global area would be much lower than it is today.  Arctic sea ice melted quickly in August and the first half of September because it was thinner than usual and winds helped push ice out of the Arctic where it could melt at lower latitudes; Antarctic sea ice has refrozen at a faster than normal rate during the austral winter.  Polar sea ice recovered from an extensive deficit of -2 million sq. km. area late last year to a +750,000 sq. km. anomaly in March 2012 before falling back to a -2.2 million sq. km. deficit earlier this month.

After starting the year at a deficit from normal conditions, sea ice area spent an unprecedented length of time near the -2 million sq. km. deficit in the modern era in 2011 (i.e., almost the entire calendar year).  Generally poor environmental conditions (warm surface temperatures and certain wind patterns) established and maintained this condition, predominantly across the Arctic last year.  The last time global sea ice area remained near 19 million sq. km. during May was in 2007, when the Arctic extent hit its modern day record minimum.  The maximum in the boreal spring the past two years was ~19.5 million sq. km.

Conditions were prime for another modern-day record sea ice extent minimum to occur in September.  Specific weather conditions helped to determine how 2012′s extent minimum ranks compared to the last 33 years, but it was the overall poor condition of Arctic sea ice that contributed to this year’s record low values.

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Call for Climate Change-Policy Paradigm Shift

9:43 am in Uncategorized by WeatherDem

(image: Ennor / flickr)

Nature Climate Change‘s most recent issue included a paper by Kevin Anderson and Alice Bows entitled, “A new paradigm for climate change” [subs. req'd].   Kevin works at the Tyndall Centre for Climate Change Research, School of Mechanical Civil and Aerospace Engineering and Alice works at the Sustainable Consumption Institute, School of Mechanical Civil and Aerospace Engineering, University of Manchester.  The discussion and arguments in the paper aren’t exactly novel if you’ve paid attention to the policy side of the climate change topic but bears examination as much as other works on the climate-policy interface, in which I am very interested.

I think the paper has some serious flaws in its assumptions, which detracts from the policy prescriptions offered.  Prime among the flaws is this:

We urgently need to acknowledge that the development needs of many countries leave the rich western nations with little choice but to immediately and severely curb their greenhouse gas emissions

The latter part of this statement simply will not happen, barring additional severe economic distress.  The first part represents progress from the scientific community: developing nations want and deserve higher living standards, of which energy is a primary input.  But developed nations cannot and will not “immediately and severely curb their greenhouse gas emissions.” There is a choice that these nations make every day: their own economies will grow and they will do so with the cheapest energy possible. Read the rest of this entry →