Wednesday, July 22, 2015

The Ice Age Cometh?

Recent media reports have claimed that a drop in solar activity will lead to a mini-Ice Age within the next 15 years.  Unfortunately, even press reports from science-related media such as Science Daily, have been riddled with errors.

Let's get the biggest one out of the way first.  Zharkova et al. (2015) did not predict a new Little Ice Age (LIA).  What they did was use principle component analysis to detect and model magnetic waves within the sun.  They found that there were two such waves, each with an 11-year cycle, that either interfered with each other when sunspot activity was low or magnified each other when sunspot activity was high.  They then ran their statistical model ahead to make a prediction for the next solar cycle and found that their model predicts that the waves should cancel each other out, resulting in their subsequent prediction that solar activity should drop to levels not seen since the Maunder Minimum.  That bit about the Maunder Minimum is what set off the media, as the Maunder Minimum coincided with the coldest time period of the Little Ice Age.

Unfortunately for the journalists and editors who made that connection and then made the claim that a new Little Ice Age would begin within 15 years, they are dead wrong.  First, multiple research papers have found that a new Maunder Minimum would shave a maximum of 0.3ºC off the expected rise in global temperatures by AD 2100 (Feulner and Rahmstorf 2010, Jones et al. 2012, Anet et al. 2013, Meehl et al. 2013).  So the world would warm by "only" 3.7ºC rather than 4ºC.  Furthermore, the impacts would be largely regional, not global, and temporary.  Ineson et al. (2015) found that the greatest cooling would fall on Europe and the eastern US during winter but that global temperature as a whole could be largely unchanged.  Once the new minimum ended, regional temperatures would warm back up.

Second, solar activity decoupled from global temperature in the 1970s.  Solar activity peaked in the late 1950s and then again around 1980 and has declined sharply since whereas global temperatures rose.  In short, global temperatures are controlled by something other than solar activity now.

Third, research shows that the Little Ice Age began and was sustained by volcanic eruptions, not solar activity (Miller et al. 2012).  And contrary to the Science Daily article, the LIA began in AD 1300, not AD 1645 as that article wrongly claimed.  The timing of the Maunder Minimum, coinciding with the coldest part of the LIA, gave the false appearance of a link between the two.

Fourth, there is a lot more CO2 and other greenhouse gases in the atmosphere now than there was during the Maunder Minimum.  The 12-month moving average for CO2 is now 399.34 ppmv.  Pre-industrial CO2 levels were around 280 ppmv, which means that there is now 1.89 W/m2 of extra energy being trapped by Earth's atmosphere that wasn't there during the Maunder Minimum.  That translates into a temperature rise of 1.53ºC, greater than the drop the Earth experienced during the Maunder Minimum.

Last, the Little Ice Age was just that—little on the global scale.  Using the global data from Marcott et al. (2013), the Little Ice Age was a mere blip compared to how temperatures have risen since.

Global temperatures over the LIA declined by about 0.2ºC over 550 years.  Temperatures have risen by 0.8ºC in the 160 years since the LIA ended.  Even if we did have another LIA, then all it would do is return global temperatures to about where they were around 1980, which is a far cry from where they were during the Maunder Minimum.

To sum all of this up, there is no new ice age coming, even if the sun does repeat the Maunder Minimum.  Instead, we can expect temperatures to continue rising as CO2 levels increase due to the 30+ billion metric tons of CO2 we spew into the atmosphere each year. 

Likely global temperature rise in the near future. The thick dashed line represents the continuation of the trend. The thinner dashed lines mark one standard deviation and two standard deviations from the trend, respectively.

Abraham Lincoln once quipped that his opponents "had their facts absolutely right but were drawing the wrong conclusion."  Those journalists who wrote that another mini-Ice Age was coming not only drew the wrong conclusion—they also got their facts absolutely wrong.

Tuesday, July 21, 2015

US versus global temperatures

One of the talking points I see (and hear) time and again here is the question "If the world's getting hotter, why is it cold here?", "here" usually referring to the eastern United States.  Another variation goes "Global warming can't be happening because US temperatures haven't risen in _____ years."  Yes, it's the good old "It's cold in my backyard so the planet can't be warming up" argument. Here's why it's dead wrong.

Friday, June 5, 2015

The "hiatus" doesn't exist.

That is the conclusion of a new study published in Science yesterday.  Tom Karl and his co-authors used a newly available database of weather station data that combined the Global Historical Climatology Network (GHCN) used by NOAA and NASA with over 40 other historical data sources, effectively doubling the size of the available land temperature data set.  They applied the same corrections for changes in location, urban heat island effect, etc as with the GHCN-only data set and used the same algorithms to calculate the global average over land.  To get a global average, they used the Extended Reconstructed Sea Surface Temperature dataset version 4 (ERSST4), which better integrates ship-based temperature data and buoy-based temperature data, and merged it with their new land data.  Karl et al. then created a third global temperature average that also fills in the gaps between weather stations in the polar regions.

Their new data set shows much higher trends than the GHCN-only data, especially since 1998.  Their analysis shows >2x the warming since 1998 (0.086ºC/decade) as the GHCN-only data (0.039ºC/decade).

Figure 1 from Karl et al. 2015 showing the trends over selected time periods as calculated using GHCN-only data (circles), their new data (squares), and their new data combined with polar interpolation (triangles).
This is mostly due to a much higher sea surface average (0.075ºC/decade versus 0.014ºC/decade) since 1998.  The upshot is that there is no statistically difference between the 1951-2014 warming rate and the 1998-2014 warming rate, meaning that the so-called "hiatus" does not exist.

The main conclusions from Karl et al. is that the appearance of a pause was due to a) a short time period (changing the period by just two years had a significant impact on the calculated trend) and b) a cherry-picked start year (1998, the warmest El Niño currently on record), and c) artifacts due to incomplete data.  This matches the main thrust of other research into global temperature data (i.e. Foster and Rahmstorf 2011, Rahmstorf et al. 2012, Rohde et al. 2013, Cowtan and Way 2014, the various Berkeley Earth papers) and various blog posts (i.e. Tamino and my own writings).

The "pause since 1998" is dead.  Long live the "pause since ______" that deniers come up with next.

Sunday, May 17, 2015

Doom and gloom or realism?

Humanity is in trouble with climate change.  A recent article in Vox by David Roberts came to that conclusion.  It begins with
"There has always been an odd tenor to discussions among climate scientists, policy wonks, and politicians, a passive-aggressive quality, and I think it can be traced to the fact that everyone involved has to dance around the obvious truth, at risk of losing their status and influence.
The obvious truth about global warming is this: barring miracles, humanity is in for some awful shit."
 The basis for that conclusion?  Total carbon emissions to date, which are closely following the RCP 8.5 curve from the IPCC.

That black curve is emissions to date.  We as a civilization are on track to take carbon dioxide levels to around 1000 ppm by 2100 AD.  The 12-month moving average of atmospheric CO2 levels shows that we're already at 398.83 and still accelerating upward.

That locks us into at least 1.53ºC of total warming as of now, assuming that the current situation wherein other anthropogenic effects (methane, aerosols, etc) continue to largely cancel each other out as has been the case for the last several decades.  At the current rate of increase, we'll blow past 444 ppmv in 2034, just 19 years from now, and be locked into at least 2ºC of warming.

The main reason Roberts is so pessimistic is that all the scenarios in which we avoided the worst of climate change assume that civilization will suddenly switch to wind power, solar energy, and other forms of energy and deploy technologies—especially carbon capture—to deal with the carbon dioxide that is already in the atmosphere.  The models also assume that humans will end the use of fossil fuels just as quickly.  Beyond those possibly overoptimistic assumptions, the sheer rate at which emissions would have to decline at this point to avoid blowing past 2ºC of total warming is  4 to 6% per year, far beyond any rate ever achieved before.  In other words, it won't be easy but, as Joe Romm wrote, it will be much cheaper and easier than trying to live in a 4ºC world.

While I share Roberts' concern and some of his pessimism, we haven't hit the point of no return yet.  I'm still hopeful that humanity can turn itself around before reaching the 444 ppmv level.  It may be hope without reason but as long as we haven't hit 444 ppmv, there's still a reason to agitate for changes in governmental policy to keep us below that level.  And yes, to the dismay of many American conservatives, it's going to take governmental action along the lines of WWII to pull this off.  We've dilly-dallied too long and allowed too much carbon dioxide to build up for individual actions to suffice.  Sorry.

Of course, as Winston Churchill quipped, "You can always count on Americans to do the right thing - after they've tried everything else."  Another way to look at it: Americans won't take climate change seriously until it affects them personally.  Here's hoping that America—and by extension the world—gets its wake-up call(s) in time.

So, what's your take on our chances?

Sunday, May 10, 2015

First look: UAH 6.0 vs UAH 5.6 vs RSS

Spencer and Christy recently released a new version (version 6.0) of the UAH satellite temperature data. To see how their data has changed, I've compared the 6.0 version to the earlier 5.6 version and compared both to RSS, similar to what I did before. All calculations were made using annual data.

The difference between UAH 5.6 and UAH 6.0 is quite dramatic, especially since 2000, and the difference has grown over time.

Difference calculated by subtracting annual version 6.0 values from the respective 5.6 values.
  Comparing both UAH versions to RSS shows that while version 5.6 was consistently warmer than RSS since 2003, version 6.0 has a tendency to run cooler than RSS since 1998.

The effect all the changes from 5.6 to 6.0 had on the calculated trend was drastic. Since 1990, the average version 6.0 trend is 0.0094ºC/year lower than the same trend in version 5.6.  For version 5.6, only the trends since 1997, 1998, and 2000 were not statistically significant.  For version 6, every trend since 1993 has not been significant.

Trend ± 95% confidence intervals for different start years.

Taking a closer look, land temperatures were nearly the same for both UAH versions.

Both versions have 2010 as the hottest year in the satellite record and show nearly the same linear trends.  Note: Unless stated otherwise, all trends are given as trend ± standard error.  For example, the two versions show nearly the same trend since 1979: 0.186 ± 0.028ºC/decade and 0.191 ± 0.028ºC/decade for versions 5.6 and 6.0 respectively.  Yes, version 6.0 shows a faster overall rate of temperature rise over land than version 5.6.  Where version 6.0 shows cooling relative to version 5.6 is over the oceans.

Here, notice how version 6.0 generally shows warmer temperatures up to 1998 than the version 5.6 and cooler temperatures afterwards?  That's the reason UAH 6.0 shows less overall warming than UAH 5.6. While UAH 5.6 shows a warming rate of 0.111 ± 0.021ºC/decade over the oceans since 1979, UAH 6.0 shows a warming rate of only 0.083 ± 0.022ºC/decade over the oceans.  Given that the oceans make up 71% of the surface area of this planet, that is enough to drop the overall global warming rate since 1979 from 0.139 ± 0.022ºC/decade in UAH 5.6 down to 0.113 ± 0.023ºC/decade in UAH 6.0.

There are a few other areas of interest to compare before I wrap this post up.  Arctic temperature trends show a major drop, from 0.441 ± 0.052ºC/ decade in UAH 5.6 down to 0.235 ± 0.042ºC/decade in UAH 6.0.

The main reason for that drop is UAH 6.0 shows warmer temperatures in the early part of the satellite record relative to UAH 5.6 and cooler temperatures in the later portion.  Finally, continental US temperatures trends declined in UAH 6.0 from 0.211 ± 0.052ºC/decade to 0.154 ± 0.045ºC/decade.

The difference in trends is not statistically significant, unlike the difference in the Arctic and the differences between temperatures is relatively minor.

In closing, I would recommend that everyone read Roy Spencer's summary of all the changes they made in UAH 6.0.  It's very informative of the challenges of accurately measuring global temperatures via satellite, including a good summary of why various adjustments to the data are necessary.

"One might ask, Why do the satellite data have to be adjusted at all? If we had satellite instruments that (1) had rock-stable calibration, (2) lasted for many decades without any channel failures, and (3) were carried on satellites whose orbits did not change over time, then the satellite data could be processed without adjustment. But none of these things are true. Since 1979 we have had 15 satellites that lasted various lengths of time, having slightly different calibration (requiring intercalibration between satellites), some of which drifted in their calibration, slightly different channel frequencies (and thus weighting functions), and generally on satellite platforms whose orbits drift and thus observe at somewhat different local times of day in different years. All data adjustments required to correct for these changes involve decisions regarding methodology, and different methodologies will lead to somewhat different results. This is the unavoidable situation when dealing with less than perfect data."
 Many of the same adjustment challenges apply to surface data, making this a useful reference for those who claim that various agencies are fudging the surface data with their adjustments.

Thursday, April 23, 2015

The view from Greenland's highest peak

It's amusing to me whenever a science denier cites the ice cores in Greenland as "proof" that global warming either a) isn't happening or b) isn't a big deal. It's a horrible argument for deniers to make. Here's why.

First, we're talking about ice cores taken from one location in Greenland. Not only is it one single location, but it just happens to be Greenland's highest point (10,660 feet/3,249 meters above sea level) and near the center of the continental glacier that covers Greenland. Guess what? It's going to be cold up there, just from the elevation alone, to say nothing of how all that ice affects the local temperature. Location matters. It's amusing that the same deniers who claim urban heat island when trying to explain away any warming trends seem to forget that when faced with factors that would decrease the rate of local temperature change.

Second, when we talk about global warming, we mean the entire planet, which is far larger than one single spot in the center of Greenland. While interesting and informative (hey, we need all the data we can get!), it ultimately says little to nothing about whether or not the entire planet is warming up and at what rate, just as readings from a thermometer in your backyard says little the change in the global average.

Third and most amusing is this: The research that at least one denier (and WUWT) tried to cite as proof that modern temperatures have yet to exceed historical temperatures (Kobashi et al. 2011) is...wait for it...a hockey stick paper! Take a look at Figure 1 from that paper:

Figure 1 from Kobashi et al. 2011

Now what does that show? Well, the top shows the past 170 years, the middle shows the last 1,110 years, and the bottom graph shows the last 4,010 years. What do you see? WUWT and other deniers focused on the fact that reconstructed temperatures were higher than the 2001-2010 average at multiple points in the past. But take a good look at the overall trend in the data, especially relative to the 2001-2010 average. What do you see? Yep. A gradual cooling trend, with a sudden reversal in the last 100 years. The same story found by Marcott et al., PAGES 2k, and other hockey stick papers.  Oops. I wonder if anyone at WUWT ever noticed that.

In short, WUWT is correct—the reconstruction does show that one location at the top of Greenland was warmer in the past. But it's a matter of trying so hard to win the battle that they end up losing the war by ignoring that the same study corroborates the warming of the past century and show that same cooling-until-the-20th-century pattern as many other studies.

Tuesday, April 21, 2015

Using NOAA's Climate-at-a-glance widget to fact-check James Taylor

Okay, I'm back.  Sorry for the lengthy gap between posts but work and losing my laptop intervened.  Now to get back in the saddle.

A reader by the pen name of cosmicomic asked several questions on my last post concerning James Taylor's claims about winter-time cooling in the US.  Since NOAA's climate-at-a-glance widget didn't work properly for him, I thought I'd post a video of what one should see as well as expound on the bogus method Taylor used.  Specifically, I'll examine Taylor claim that winters in the US have cooled, with the cooling trend dating back to 1930.

First, a very brief tutorial by yours truly on using NOAA's widget and what you should see when you do:


Now, Taylor's claim that US winters have cooled since 1930 is already in trouble. The simple linear regression model done by the widget shows that US winters have warmed by an average of +0.18ºF/decade since 1930. ARMA time series regression shows that the warming trend since 1930 is statistically significant (p = 0.03015). Dropping 2015 (since Taylor was writing about the 1930-2014 time period) only lowers the trend since 1930 to 0.17ºF/decade (p = 0.041), still a statistically significant increase.

So, what did Taylor do to come up with his "cooling since 1930" claim? Simple. He played "connect the dots." It's really easy to do (David Rose of the British tabloid The Daily Mail is a master of it). Just find a year that was warmer than the end year (in this case 2014), draw a line connecting that year to the end year, and claim "Cooling since _____!" In Taylor's case, just connect 1930 to 2014.

Voila! Instant cooling trend and you don't even have to bother with all that pesky time-series analysis, ARMA regression, and the like. All you need is what you learned in kindergarten. Of course that only works to climate deniers' favor  if the end point is lower than the starting point. And if you ignore everything except the beginning and end points. And if you ignore pretty much everything a beginning stats student learns in the first semester. get the idea.

In short, Taylor's "method" is utterly bogus. But he won't let such a trifling detail stop him.