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Bridging climate science, citizens, and policy


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More Discussion on Warming “Hiatus”

After a lengthy absence during which I studied for the most challenging mental exercise I’ve ever faced – departmental Comprehensive Exams – I’m going to kick off 2014 with another discussion about the early 21-century warming “hiatus”.  There is good reason for this: the climate is complex and understanding the individual parts remains as active research, to say nothing of how those parts interact, which adds complexity upon complexity.  It also gets me back in the swing of writing again.

The motivation for this piece is a new paper, “An apparent hiatus in global warming?”.  Here are important parts of the abstract (you can read the entire abstract at the link):

Global warming first became evident beyond the bounds of natural variability in the 1970s, but increases in global mean surface temperatures have stalled in the 2000s.  Increases in atmospheric greenhouse gases, notably carbon dioxide, create an energy imbalance at the top-of-atmosphere (TOA) even as the planet warms to adjust to this imbalance, which is estimated to be 0.5–1 W m−2 over the 2000s. […] An energy imbalance is manifested not just as surface atmospheric or ground warming but also as melting sea and land ice, and heating of the oceans. More than 90% of the heat goes into the oceans and, with melting land ice, causes sea level to rise. For the past decade, more than 30% of the heat has apparently penetrated below 700 m depth that is traceable to changes in surface winds mainly over the Pacific in association with a switch to a negative phase of the Pacific Decadal Oscillation (PDO) in 1999. Surface warming was much more in evidence during the 1976–1998 positive phase of the PDO, suggesting that natural decadal variability modulates the rate of change of global surface temperatures while sea-level rise is more relentless. Global warming has not stopped; it is merely manifested in different ways.

Some important notes here.  Greenhouse gases consistently increased during the 20th century, with increasing rates in recent decades.  But how do those GHGs affect the climate?  They emit radiation back towards the Earth’s surface, but it takes time for that radiation to manifest as detectable heat.  It’s a slowly accumulating effect, which other processes and phenomena influence.  To be more specific, the Earth’s surface temperature (land and ocean) shows the effect of that slow accumulation decades later.  This decade’s surface temperatures are largely the result of GHG concentrations from 20-30 years ago.  Which means that today’s concentrations will largely affect surface temperatures 20+ years from now, not today.

Let’s take a look at one of the study’s graph’s – global mean surface temperature anomalies from 1850-2012.

 photo GlobalMeanTemperature-TrenberthampFasullo2014_zps15374d73.jpg

Figure 1. Global mean surface temperature anomaly (1850-2012; Trenberth & Fasullo) as observed by the four most used datasets.

After a rapid rise in the 2nd half of the 20th century, it does indeed appear as though warming has paused since 2000.  But I just wrote that GHG concentrations increased throughout the 20th century and into the 21st.  So why does the “pause” appear in the temperature record?  Because of other climate processes, in this case natural processes that I’ve also written about (see here and here).

 photo Global12-monthrunningmeansurfaceTanomaly-TrenberthampFasullo20140113_zps3f9a0298.jpg

Figure 2.  Global mean surface temperature anomaly (12-month running mean) with El Nino (orange) and La Nina (blue) events highlighted.

Figure 2 shows how the biggest high-frequency climate oscillation impacts global mean surface temperature anomalies.  Following the record-setting 1997-1998 El Niño, annual temperature anomalies stayed primarily within +0.6 to +0.7C.  The paper hypothesizes that the 97-98 El Niño initiated a change in longer-term oscillations – namely the Pacific Decadal Oscillation (related to the Interdecadal Pacific Oscillation, which impacts my own research).

 photo PDOIndex1950-2013TrenberthampF20140113_zpse6e432fa.jpg

Figure 3. Time series of Pacific Decadal Oscillation Index (1950-2013).

Phases characterize the index: warm (1977-1998) and cool (1948-1976 & 1999-current).  Look back at Figure 1 and the PDO’s effect on global mean surface temperature anomalies is clear: less warming is present during the cool phases and more warming during the warm phase.  Now, this analysis is limited by the relatively short observational period, but researchers are teasing out PDO effects from paleoclimatic studies going back hundreds of years.  The PDO’s cool phase is characterized by cooler than normal eastern Pacific sea surface temperatures.  Averaged out over 10-30 years, the cool phase looks remarkably similar to La Nina.  Conversely for the warm phase, the eastern Pacific is much warmer than normal and resembles a long-term El Niño.

Now for some complexity.  The short-lived El Niño/La Niña events occur on top of the PDO signal.  So the Earth can have a long-term cool phase (negative PDO) and have both warm and cool ENSO phases (El Niño/La Niña) on annual to interannual timescales.  Look at Figure 2 again to see the additive impacts.  The 1997-98 El Niño occurred at the end of the last PDO warm phase, but also during a warming trend whose timescale exceeds the PDO’s (anthropogenic climate change).  Four recent La Niñas occurred during the current negative (cool) PDO phase within the past 10 years (see Figure 2).  Is it any wonder then that global mean surface temperatures haven’t risen at the same rate they did during the 1977-1998 period?

So what does this mean going forward?  First of all, I disagree with the 2nd half of Trenberth’s statement: “This year or later, it’s possible that El Niño will occur again in the Pacific. Will that trigger another change in the PDO, that in turn could trigger a resurgence in global surface temperature warming? Only time will tell, Trenberth explained.”  Given the historical PDO record, I seriously doubt the next El Niño will switch the PDO phase back to positive (warm).  The PDO has been in its current negative phase for only 14 years or so now.  It’s more likely that this negative phase will continue for at least the next 5 years.  I wouldn’t be surprised if it continued for the next 10-15 years.  Which doesn’t mean global temperatures won’t rise; it means they would likely rise at a slower rate than they did during the late 20th century.  When the next PDO positive phase occurs, global temperatures will likely show that shift by increasing at a faster rate than during the past 15 years.

Lastly, just because the Earth’s surface hasn’t warmed quite as much as expected in the past 10-15 years doesn’t mean the heat disappeared.  What you heard as a kid was true: energy cannot be destroyed, only changed.  The heat energy emitted by GHGs during the past 30 years went to a place humans don’t measure very well or very much: the deep ocean, as this graph shows:

 photo Ocean_heat_content_balmaseda_et_al_zps23184297.jpg

Figure 4.  Anomalous ocean heat energy locations since the late 1950s.  The purple lines in the graph show how the heat content of the whole ocean has changed over the past five decades. The blue lines represent only the top 700 m and the grey lines are just the top 300 m.  Source: Balmaseda et al., (2013)

This graph shows that during the global warming “pause” period (1999-current), the ocean below 700m absorbed the majority of the heat of the entire ocean system.  You can also quite clearly see the anomalous heat content of recent years.  This increased oceanic heat content will manifest itself in upcoming decades and centuries.  Sea levels will rise because warmer substances occupy more volume than cooler substances.  That effect alone threatens the majority of the Earth’s human population.  It also threatens frozen water reservoirs: the globe’s ice caps.  As they melt at an increasing rate throughout this century, global sea levels will rise even further.  As warmer deep ocean water returns to the surface and interacts with a warmer atmosphere which can hold more moisture and therefore heat, the heat will eventually transfer to the atmosphere where we can more regularly measure it.  So aside from the natural climate oscillations discussed above (ENSO & PDO), much of this heat will affect us at some point.

Will we be ready for those impacts?  Contemporary examples suggest no, but municipalities are taking already visible threats more seriously every day.  Those local efforts will guide actions at higher levels of government and society.

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Research: Recent Warming Rate May Be Higher Than Previous Estimates

Posts here slowed down for a bit due to my participation in a poster symposium, a research group presentation, studying for comprehensive exams, and writing thesis chapters.  I will continue to post at a lighter than normal rate until February.

Climate science is a notoriously complex topic.  We don’t measure the climate everywhere with high precision.  Analysis methods have advantages and disadvantages.  Signals take time to manifest, record, and analyze in proper context.  A new paper in the Quarterly Journal of the Royal Meteorological Society, “Coverage bias in the HadCRUT4 temperature series and its impact on recent temperature trends” by Cowtan and Way illustrate the difference that individual analysis techniques present to researchers.

At issue is the recent perceived slowdown in global surface temperature rise.  Skeptics seized on this situation as their latest new argument that global warming is a hoax.  Science is a slowly evolving endeavor.  Climate change advocates cite decades, centuries, and millenia data to argue that global warming is man-made and accelerating.  Skeptics used ~15 years data to argue the opposite.  Cowtan and Way examined surface temperature data using a method combination, not just one, as groups like Hadley and NASA do.

Here is the study’s result in a nutshell: Applying multiple analysis techniques to a combination of data reduces the bias present in the individual data and techniques.  The authors posit that the Hadley dataset is cool biased because they omit 16% of the Earth’s surface where land-based observations are few to nonexistent.  Here is a comparison of 1979-2012 temperature trends using Hadley’s original data and Cowtan and Way’s combination:

 photo Globaltemptrend1979-2012MetOffice-vs-CowtanWay13_zps2aed74bb.jpg

Figure 1 – Met Office vs. Cowtan & Way (2013) global surface temperature coverage and 1979-2012 trend.

Where is the lack of Hadley data?  It is where the most warming occurred the fastest: across the Arctic.  Even the areas in Africa and South America omitted in the Hadley analysis show warming.  We should all know Antarctica’s condition by now: some areas are warming, some are cooling; overall there is little trend one way or the other over this time period.  But Cowtan and Way include all areas.

How did Cowtan and Way achieve their result?  To head off an obvious skeptic’s argument: they didn’t just make it up.  They employed recognized and widely used techniques.  They employed the first, “kriging“, over land and ocean areas.  This method fills in data points between observing stations and includes a confidence interval around the interpolated point.  One can assess the bias in the result by removing observing stations, performing the interpolation, then using the removed data as verification points.  I’ve used this method in my own past research.

Cowtan and Way also employed University of Huntsville satellite surface temperature data along with available surface data to fill in gaps in missing areas.  Interestingly, Cowtan and Way’s analysis demonstrates that the kriging method worked best over the ocean and the hybrid method worked best over land.  The bottom of Figure 1 and Figure 2 show the result spatially and temporally, respectively.

 photo Globaltemptrend1979-2012MetOffice-vs-CowtanWay13-2_zpsaf60604b.jpg

Figure 2 – Time series of temperature anomalies in the HadCRUT4 data (black solid line), null reconstruction (red dashed line), Kriging reconstruction (green dashed line), and hybrid reconstruction (blue dashed-dotted line).

The bottom panel of Figure 2 shows the 60 month moving average of HadCRUT4 and reconstructed data.  The hybrid result (blue dashed-dotted line) shows a lower anomaly decrease in the past 10 years than the original HadCRUT4 data, which is biased cool due to lack of data points in warming portions of the globe.  There is almost no discernible difference between the Kriging and hybrid reconstruction time series data in the past 10 years.  The 60 month moving average removes high-frequency effects such as the annual cycle and higher frequency ENSO.  The result shows lower frequency signals, such as global warming.

So what processes occurred in the past 10 years to shift the temperature anomaly trend from sharply positive to less positive?  I’ve covered all of them: increased heat uptake by the ocean, especially the deep ocean: Research: Ocean Heat Content Continued to Rise Through 2010, On the global surface warming “pause”, NASA & NOAA: August 2013 4th Warmest Globally On Record; increased small to moderate volcanic activity and reduced solar maximum activity: Research: Volcanic Aerosols Largely Responsible for Recent Warming Slowdown.  Lastly, the Cowtan and Way paper demonstrates that data coverage and interpolation techniques impact results and conclusions.

Compared to HadCRUT4’s 0.046°C (±0.063) decade-¹ 1979-2012 trend, NASA’s 0.080°C (±0.067) trend, NOAA’s 0.043°C (±0.062) trend, and NCEP-NCAR’s 0.178°C (±0.107) trend, Cowtan and Way’s analysis resulted in a 0.119°C (±0.076) trend.  This means the perceived recent warming slowdown could be less than previously thought (higher trend with smaller bias).  Note that all datasets and analysis techniques indicate 1979-2012 warming.  But if you care about how much warming, this paper provides a compelling argument that the significant entities engaged in up-to-date analysis should take a hard look at their internal methodology and update them as needed.

This paper’s results also mean that a need for robust climate policies at every level of government still exists.  Relatively minor methodology adjustments don’t preclude policy development and implementation.  Policymakers may not want to hear that given their propensity to hand off decision-making to outside experts.  The scientific message has not and will not change.


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Globe’s 19th Warmest January in 2012

January 2012 was the globe’s 19th warmest on record, according to NOAA, which is pretty much what one would expect given the prolonged La Niña conditions dominating the tropical Pacific and the fact that we’re still climbing out of the last solar minimum.  The characterization could be made that despite the cooling being exerted, the globe still ended up being warmer than more than 110 other January’s!

It is useful to keep in mind when reading about these type of circumstances that there are multiple signals occurring at the same time (solar, ENSO, AGW, etc.) and the state of global temperature (or any other variable) at any one point in time is but a snapshot within larger trends.


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Changes In The Arctic

I’ve written about Arctic sea ice conditions for a couple of years now. As I’ve written new posts, I’ve tried to include information regarding the science behind the conditions being written.  2010 was a particularly bad year for Arctic ice, as conditions were recorded to be well below average conditions for months at a time.  Arctic ice in September 2010 challenged the record low minimum extent observed in the modern era in 2007.  My summary conclusion after paying attention to Arctic sea ice is this: the Arctic has entered into a new climatic regime.  Conditions are now regularly quite different than those observed in the past couple hundred years.  I’m going to provide a broader look at this topic in this post.

When I have written about climatic changes, especially in the context of the Intergovernmental Panel on Climate Change’s 4th Assessment Report Physical Science Basis (IPCC 4AR WG1), I have increasingly mentioned the disturbing fact that the IPCC’s projections were far too conservative to be of real use to policy makers.  The reason is both simple and complex.  Simply put, the IPCC focused on moderate greenhouse pollution scenarios that were better researched.  The biggest problem with that is the globe’s actual emissions path is following the worst-case scenario (A1FI) considered by the IPCC 4AR (courtesy of Hansen and Sato; data through 2010):

Of greater complexity is the “better researched” part of my statement.  Critical feedbacks were largely kept out of climate model runs leading up to the 4AR.  There is nothing intrinsically wrong or manipulative about this.  Those feedbacks remain less researched and therefore less understood than other processes included in state-of-the-art model efforts.  That situation is improving, as feedbacks are coming under increasing scrutiny.  This is where politics intrudes: somebody has to fund that research.  There was a strong effort during most of the past 10 years to slow down or stop this kind of climate research.  Budgetary pressures moving forward will cause potential future research to be shelved when it’s needed most.

Back to the IPCC 4AR.  One of the problems with relying on scenarios that don’t accurately reflect the true state of the climate system is projections are starting to look overly cheerful.  Take Arctic sea ice extent as an example.  From the 2009 Copenhagen Diagnosis, we can see that not only does the mean of the IPCC models over-project the extent of September Arctic sea ice only a few short years after making the projections, but the worst-case scenario wasn’t able to capture how low sea ice extent would get prior to 2010 (data through 2008); [h/t msobel for reminding me this graph existed].

September 2009’s extent was similar to 2008’s.  2010’s looked more like 2007’s, which is represented by the lowest point of the red line in the above graph.  In other words, the observations time series continues to record values substantially lower than the bottom of the IPCC models’ range.  Scientists (and others) love to ask, “Why?”  So, the question should be, “Why were the IPCC models so far off on this projection?”  A quick note: a growing number of other kinds of projections are showing similar signs of being worse than projected much sooner than was thought to be the case.  I will discuss some, but not all, of the factors involved in this phenomenon.

I’ve already shown the annual growth of CO2 emissions over the past 50 years.  That, of course, is only part of the story.  Since CO2 isn’t scrubbed from the atmosphere very quickly, CO2 concentrations have risen with that growth of CO2 emissions.  Here is the state of atmospheric CO2 concentrations measured at Mauna Loa, Hawai’i as of early February 2011:

(Courtesy Tans et al., NOAA/ESRL web site)

Up and up it goes.  2010’s average CO2 concentration was 389.69ppm.  That will be the last time in a long time that the concentration will be below 390ppm.  Today’s concentration is higher than at any point during the past few hundreds of thousands of years.  Oh yeah, I almost forgot, the last time concentrations were above 400ppm for an extended period of time (somewhere between 400 and 560ppm), the Greenland ice sheets collapsed.  That’s because there is a melting ice/warmer air feedback that occurs around Greenland.  The problem?  Nobody knows exactly where the tipping point leading to collapsing ice sheet exists.  Since we’re only 10ppm  and 5 years away form 400ppm, does anybody seriously want to continue gambling?  After all, it’s going to take quite some time to get that concentration back below 400ppm; more time will be required the longer we wait.

CO2 is being emitted into the atmosphere faster than it is being removed.  The concentration of CO2 is therefore increasing.  As a result of very basic physical laws, more and more solar energy is accumulating in Earth’s climate system.  Part of this energy is manifesting as increased surface temperatures:

This graph shows 5-year and 11-year running averages of global temperatures as analyzed by NASA’s James Hansen.  Within this data, something interesting is occurring.  And it didn’t become obvious until Hansen published a different kind of temperature anomaly graph.  Instead of averaging the entire globe’s temperatures together, Hansen averaged temperatures over different latitude bands together:

If it’s too hard to make out all the little details, check out this web page, where you can click on a PDF which shows a much larger version.  I’m going to concentrate on the top two boxes in this graph, which show temperature anomalies for five zones (upper-left) and for the two polar zones (upper-right).

The first thing I want to point out is the period between 1940 and 1980.  This period has been cited recently by climate zombies as one reason not to listen to climate scientists.  According to the zombies, predictions were made in the 1970s about global cooling.  Nothing exists in the scientific literature supporting this claim, of course.  What scientists did say in the 1970s was the recent warming trend was no longer evidenced and they wondered what could be causing it.  Without getting further into the minutiae, the top two time series show where the global signal originated from: the Arctic.  It was the zone that showed the strongest signal that looks similar to the signal seen in the global temperature anomaly time series.  Since the 1970s, the Arctic’s surface temperatures have warmed more than any other zone.  You can see that in 2010, the Arctic temperature anomaly was greater than 3.6F (2C).  The northern mid-latitudes (23.6°N to 64.2°N, or the zone in which most of us live) has “only” warmed by just under 1.8F.  The northern mid-latitudes showed a slight cooling from the mid-1960s to the mid-1970s, but if you look at the time series on the bottom-left, the scale is much smaller than the Arctic graph in the upper-right.

So that’s what’s happened in the lowest part of the atmosphere above the Arctic: the greatest warming of any zonal area on Earth since the 1880s.  Arctic sea ice, of course, rests on water – the Arctic Ocean, to be precise.  Something has been occurring to the Arctic Ocean at the same time that the atmosphere above the ice has been steadily warming.  Unfortunately, it’s the same phenomenon: water entering the Arctic from the Atlantic is warmer than it has been at any point in at least the past 2,000 years.  This water is 3.5F warmer today than it was one century ago.  It is 2.5F warmer today than it was during a favorite time period for climate zombies, the Medieval Warm Period, during which Europe warmed while most of the rest of the globe didn’t see much change.  But even if the effect was global, as they wish it was, conditions are warmer today by a substantial margin.  Not only that, but the volume of water entering the Arctic from the Atlantic has also increased over the past century.  If the same volume of water that was warmer was the situation, that would be bad enough.  But significantly more water that is significantly warmer than similar water was 100 years ago is a double whammy.  What this mean is Arctic ice has a harder time forming along the edge of the ice pack on a year-to-year and decade-to-decade basis.  This is evident in the following graphic:

(courtesy Robert F. Spielhagen, Science)

The red arrows represent flow direction of Atlantic water entering the Arctic Ocean at depth.  The white arrows represent flow direction of ice exiting the Arctic Ocean at the surface.  The solid white line represents the average sea ice coverage for April from 1989 to 1995.  The broken white line represents the average sea ice coverage for April from 1963 to 1969.

Why are the time series and study results relevant to the comparison of ice extent observations against IPCC model projections?  Because they represent only a small number of examples of how increasing understanding of the Arctic has occurred in recent years and that’s problematic when interpreting the IPCC’s results.  I haven’t covered how the warming observed in the Arctic so far is thawing permafrost both on land and underwater, which is projected to release 1 Billion tons of carbon into the atmosphere yearly by the 2030s – and how such a process likely won’t be included in the IPCC 5AR.  Additionally, most of that carbon will be released as methane, which is 72 times as efficient a greenhouse gas over a 25 year period than CO2.  I haven’t covered how the retreat of Arctic sea ice is causing additional solar energy to be collected by dark sea water instead of being reflected back into space by white ice – and how such a process also isn’t included in today’s climate models.  I haven’t covered how over 80% of the solar energy absorbed in the past couple hundred years is currently stored in the world’s oceans, mostly at depth.  When that warmer water rises to the surface, it will interact with a warmer atmosphere in ways that are not completely understood.  Of course, warmer waters means Arctic sea ice will have even less of a chance of existing year-round in tomorrow’s world.

To some extent, I have talked about the dangers involved with spending most of our research time on moderate emission/warming scenarios, when our actual emission scenario is closer to the worst-case considered in the 2007 report.  But all of the feedbacks I’ve discussed so far are lacking from all of the emission scenarios.  What will happen when those feedbacks are included?  Instead of “5.0 °F with a likely range of 3.1 to 7.9 °F” for the A1B scenario or “7.2 °F with a likely range of 4.3 to 11.5 °F” for the A1FI scenario from the 4AR by 2100, the globe could experience 10-13°F warming by 2100.  Long before then, the Arctic will likely have attained a new stable climate; one that is quite different from the climate present during most of our species’ existence.

The Arctic has entered into a new regime.  Even climate scientists are playing catch-up right now, which means the American public is way behind in understanding what changes in the Arctic mean to them.

Cross-posted at SquareState.


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NASA & NOAA: Global September Temperatures Nearly Broke All-Time Record

In the past week or so, NASA released data and NOAA released a report confirming climate activists’ fears: 2009 is going to challenge global temperature records.  There are a number of reasons this is especially troubling to me, which I’ll get to below.

First, the news is this.  Two independent scientific agencies confirm that September 2009 had the 2nd highest surface temperatures on record.  Dating back to 1880, the only warmer September occurred in 2005.  From NOAA: the combined global land and ocean surface temperature was 1.12 degrees F above the 20th century average of 59.0 degrees F.  NASA’s measurement, probably the best in the world, indicated a 1.17F anomaly, very much in line with NOAA’s calculation.

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April 2009 5th Warmest on Record – NOAA

The globally-averaged land and sea surface temperature for April 2009 was the fifth-warmest in the past 130 years, according to a NOAA report.  This occurred as the El-Nino/Southern Oscillation phenomenon moved from a cold phase (La Nina) to a neutral phase.   The second graph on the page I’ve linked to shows where the warmest anomalies were found: eastern Russia, Europe and southern South America.  Those of us in the middle third of the U.S. (Rocky Mountains to the Mississippi River valley) experienced cooler and wetter conditions than are normally found.  In the Front Range of Colorado, a winter-long drought was eased by a pretty wet April.

The anomalies during April were +1.00°C (+1.80°F) for land only, +0.44°C (+0.79°F) for the ocean only and +0.59°C (+1.06°F) for land and ocean combined.  These anomalously high temperatures occurred during the end of a La Nina, which tends to depress temperatures, as well as during the most extensive solar minimum in over 100 years.  Many climate change deniers cite solar cycles as the most important contributor to climate variability.  If the 5th warmest temperatures in recent history were recorded during the most intense solar minimum in recent history, what do folks think will happen when the solar cycle transfers towards its maximum?  What will happen when the next El Nino occurs?  Will temperatures somehow decrase globally?  I don’t think so.