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:

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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This is the week to publish lots of interesting events and articles apparently.  I have a number of things I would love to post about, but only so much time.  Here is one that relates directly to something I posted on earlier: warmest La Niña years.  Just a few short weeks after NOAA operations wrote that 2012′s La Niña was the warmest on records, NOAA researchers announced they recalculated historical La Niñas because of warming global temperatures.  NOAA confirmed something that occurred to me while I was writing that post: eventually, historical El Niños will be cooler than future La Niñas.  How then will we compare events across time as the climate evolves?  The answer is simple: redefine El Niño and La Niña.  Instead of one climate period of record, compare historical ENSO events to their contemporary climate.  In other words, “each five-year period in the historical record now has its own 30-year average centered on the first year in the period”: compare 1950-1955 to the 1936-1965 average climate; compare 1956-1960 to the 1941-1970 average.  This is different from the previous practice in which NOAA compared 1950-1955 to 1981-2010 and compared 2013 to 1981-2010.  The 1950-1955 period existed in a different enough climate that it cannot be equitably compared to the most recent climatological period.

Figure 1. “The average monthly temperatures in the central tropical Pacific have been increasing. This graph shows the new 30-year averages that NOAA is using to calculate the relative strength of historic El Niño and La Niña events.”

I want to point out something on this graph.  Is long-term warming evident in this graph?  Yes, there is.  But note they plot the breakdown by month.  The difference between 1936-1965 and 1981-2010 in October is >1°F.  Meanwhile, the same difference in May is ~0.5°F.

Here is the effect of NOAA’s change:

Figure 2.  3-month temperature anomalies in the Nino-3.4 region.   (Top) Characterization of ENSO using 1971-2000 data.  (Bottom) Same as top, but using 1981-2010 data.

NOAA’s updated methodology resulted in the identification of two new La Niñas: 2005-06 and 2008-09.  The reason is warmer temperatures in the most recent decade than the 1970s (it sounds obvious when you say it like that).  That warming masked La Niñas with the old methodology.  It also means that the 2012 La Niña is no longer the warmest La Niña, as I related from the National Climatic Data Center last month:

Figure 3. Anomalies of annual global temperature as measured by NOAA.  Blue bars represent La Niña years, red bars represent El Niño years, and gray bars represent ENSO-neutral years.

That record will now go down as a tie between 2006 and 2009, with 2012 coming in a close third.  This situation is analogous to the different methodologies that NOAA and NASA use to compute global temperatures and where they rank individual years.  Records might differ because of methodological differences, but the larger picture remains intact: the globe warmed in the 20th and so far in the 21st centuries.  That signal is apparent in many datasets.  Within the week, I’m sure we’ll hear from GW skeptics that La Niña years have been getting cooler since 2006.  Here is what is most important: 2000s La Niñas were warmer than 1990 Niñas, which were warmer than 1980 Niñas, etc.

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.

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.

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

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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):

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

Here is the similar image from January 9, 2013:
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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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According to data released by NASA and NOAA this week, July 2012 was the 12th and 4th warmest July (respectively) globally on record.  NASA’s analysis produced the 12th warmest July in its dataset; NOAA recorded the 4th warmest July in its dataset.  The two agencies have slightly different analysis techniques, which in this case resulted in not only different temperature anomaly values but rather different rankings as well.

The details:

July’s global average temperatures were 0.47°C (0.85°F) above normal (1951-1980), according to NASA, as the following graphic shows.  The warmest regions on Earth coincide with the locations where climate models have been projecting the most warmth to occur for years: high latitudes (especially within the Arctic Circle in July 2012).  The past three months have a +0.56°C temperature anomaly.  And the latest 12-month period (Aug 2011 – Jul 2012) had a +0.50°C temperature anomaly.  The time series graph in the lower-right quadrant shows NASA’s 12-month running mean temperature index.  The recent downturn (post-2010) is largely due to the latest La Niña event (see below for more) that recently ended.  As ENSO conditions return to neutral or even El Niño-like, the temperature trace should track upward again.

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

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I’ve written a couple of posts on climate change basics (Gases, Forcing & Surface Temperature and Energy & Projections) that described how energy enters and moves through the climate system and some physical ramifications of emitting greenhouse gases.  This post will build on those in an important way by examining what is very likely to happen to the base climate system in response to increasing carbon emissions.  The operative word that is used throughout is: permanency.  The climate system has so far been slightly altered by our species’ emissions.  Most of the effects of that alteration won’t go away for hundreds of years.  As humans emit additional emissions, the effects grow.

For all intents and purposes, as far as our species is concerned, the climate system’s alteration will not go away for a long, long time – on the order of thousands of years.  That’s permanency as far as we’re concerned.  Or, as the paper I cite puts it: it’s irreversible.  Conditions will very likely not return to those we’ve experienced in our lifetimes and in the past few thousand years for many thousands of years into the future.  That’s the cold, hard scientific truth of the situation.  Now, people can decide for themselves whether such irreversibility or permanency is a “good” or “bad” thing – I won’t make normative judgments for anyone else but myself.  I don’t consider such a change a “good” thing.  The effects I will describe here are significant, but they are only those that are easily projected.  Many other effects that haven’t been considered or experienced by our species will almost certainly fall out as a result of projections discussed here.  Our civil institutions are not well equipped to handle even the first-order effects, let alone the compounding influence of effects upon effects.

On a personal note, I will not describe things as ‘catastrophic’ anymore.  I have hinted at this in some posts I’ve written in the past few months without much explanation.  The primary reason for this is using such language simply turns people off from considering the material.  I think we need more people engaged on this topic, not less, and will consider scientific results of language and framing as much as I consider climate science results (a post dealing with this specifically is in the works).  That said, I will continue to not spend many resources to engage the ideologically driven skeptic community.  They simply have a different worldview than I do and neither party will convince the other that their side is “correct”.  One goal of this blog is to inform those who are interested and to have civil, productive discussions of peer-reviewed climate science and the political/policy implications of that science.

So, before I delve into some details, words like `permanency` and `irreversible` will be used more frequently on this blog in the future.  I will not use words like catastrophic.  On that note …

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According to data released by NASA and NOAA this week, June 2012 was the 4th warmest June globally on record.  NASA’s analysis produced the 4th warmest June in its dataset; NOAA recorded the 4th warmest May in its dataset.  The two agencies have slightly different analysis techniques, which actually helps to reinforce the results from each other.

The details:

June’s global average temperatures were 0.56°C (1.01°F) above normal (1951-1980), according to NASA, as the following graphic shows.  The warmest regions on Earth coincide with the locations where climate models have been projecting the most warmth to occur for years: high latitudes (especially within the Arctic Circle in June 2012).  The past three months have a +0.59°C temperature anomaly.  And the latest 12-month period (Jul 2011 – Jun 2012) had a +0.52°C temperature anomaly.  The time series graph in the lower-right quadrant shows NASA’s 12-month running mean temperature index.  The recent downturn (post-2010) is largely due to the latest La Niña event (see below for more) that recently ended.  As ENSO conditions return to normal, the temperature trace should track upward again.

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

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From the top, I want to include important context for the research results I am presenting.  This research is based on peak warming of only either 1.5°C or 2°C.  It is my educated opinion that such goals are unrealistic.  Prevention of warming past 2°C is no longer a viable option based on our species’ history of burning carbon-intensive fossil fuels as well as the medium- to long-term future, which doesn’t promise much of a difference.  Furthermore, as I have stated numerous times in the past year, policy discussion would be better served if scientists would conduct research on developments that are much likelier to occur and not the world they want to see (i.e., higher vs. lower emissions scenarios).  That said, this research fulfills an important role in the overall discussion because I think some of the results can be used as a “floor” – conditions are likely to reach higher magnitudes than those found in this and similar papers.

Michiel Schaeffer, William Hare, Stefan Rahmstorf & Martin Vermeer’s Nature paper was published on June 24, 2012.  They examined sea-level rise in response to warming scenarios using a semi-empirical model.  By 2100, global sea-level rise would be ~60cm above the 2000 level if global GHG emissions were zeroed by 2016.  This is an obvious fantasy world, but it provides a useful benchmark for other scenarios the scientists examined.  The reason sea-level rise would continue through the 21st century even if we haled emissions completely in the next 3-4 years is the response of the climate system to the anthropogenic forcing imparted on it through the 20th and early 21st centuries.  If 1.5°C or 2°C warming is not exceeded, global sea-level rise would be 75-80cm above the 2000 level.  The authors also report that unmitigated emissions could result in 100cm rise above 2000 levels.  It is important to note that 20th century sea level rise has been estimated to be ~20cm.  It doesn’t require much thought to realize that the rate of sea-level rise has increased throughout the 20th century and continues to do so in the 21st.  Moreover, it is clear that since we will most likely warm beyond 2°C, the 75-100cm projection can be viewed as a reasonable estimate for a “floor”: actual sea-level rise could be greater than this.

The authors go on to estimate global sea-level rise by 2300.  Since the world won’t end in 2100, nor our civilizations (though they will be forced to adapt to a changing world), projections out to 2300 are useful to gain an understanding of the long-term effects of our actions.  By 2300 a 1.5°C scenario could result in peak sea level at a median estimate of 1.5m above the 2000 level. The 50% probability scenario for 2°C warming would see sea level reaching 2.7m above the 2000 level and still rising at about double the present-day rate.

That last sentence is important to understand because of 2 factors.  The first is the 50% probability descriptor and the second is the extreme difficulty in keeping warming at or below 2°C.  Even if we were to keep warming at or below 2°C, there are realistic scenarios in which sea-level rise exceed 2.7m in the year 2300.  Beyond that, 2°C acts more as a floor in the real world than a ceiling in the fantasy world that continues to garner research focus.  Our historical emissions values were closer to the higher end of the IPCC AR4′s range than the lower – or put another way, 4°C looks likelier to occur by 2100 than 2°C at this point because our emissions more closely resemble the A1B or A2 scenario.  The following graph shows the AR4′s global surface warming projections by scenario.  Note that the A2 scenario didn’t run all the way to the year 2300, but the B1 and A1B scenarios were.  The equilibrium temperature under the A2 scenario is obviously higher than that of the A1B scenario, but left unprojected in previous work.

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The state of global polar sea ice area in early July 2012 has once again fallen significantly below climatological normal conditions (1979-2009).  Arctic sea ice loss is solely responsible for this change in condition since last month.  Arctic sea ice melted quickly in June 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 near normal rate during the late austral autumn and early 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 -1.8 million sq. km. deficit.

After starting the year at a deficit from normal conditions last year, sea ice area spent an unprecedented length of time near the -2 million sq. km. deficit in the modern era in 2011.  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. through 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 are prime for another modern-day record sea ice extent minimum to occur in September.  Specific weather conditions over the next two months will determine how 2012′s extent minimum ranks compared to the last 33 years.

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