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Earth Matters

Fine Particulate Maps With and Without Dust

June 23rd, 2015 by Adam Voiland

Fine particulate matter (PM2.5) for 2010-2012 with dust and sea salt included. Visualization by Josh Stevens. Data from van Donkelaar et al. 


Fine particulate matter (2.5) concentration for 2010-2012 without dust and sea salt included. Data from van Donkelaar et al.

If you saw our June 22 Image of the Day with global maps of fine particulate matter (PM2.5), you may have noticed large concentrations over the Sahara Desert and the Arabian Peninsula. With vast deserts in these areas, it’s not a surprise that the satellites detected so many particulates. Winds regularly send plumes of dust blowing over the region and even to Europe and the Americas.

However, it isn’t clear how damaging dust particles are to human health in comparison to other types of fine aerosol particles (such as those produced by burning fossil fuels or biomass burning). Several teams of epidemiologists have looked for associations between outbreaks of Saharan dust and health problems, but the results have been mixed. A literature review published in 2012 summarized the state of the science this way: “The association of fine particles PM2.5, with total or cause-specific mortality is not significant during Saharan dust intrusions. However, regarding coarser fractions PM10 and PM2.5-10, an explicit answer cannot be given. Some of the published studies state that they increase mortality during Sahara dust days while other studies find no association between mortality and PM10 or PM2.5-10. The main conclusion of this review is that health impacts of Saharan dust outbreaks needs to be further explored.”

Since dust is natural and may not have significant effects on human health, the team of Dalhousie University scientists who developed the global PM2.5 exposure maps prepared two versions of their data. One shows total PM2.5 concentration (top map above) globally; the other shows PM2.5 excluding contributions from dust and sea salt (bottom map). Notice how much less PM2.5 appears in northern Africa when dust is excluded.

To get a sense of how PM2.5 concentration (excluding dust and sea salt) has changed between 2000 and 2010, see the map below. Notice that while PM2.5 has decreased over North America and Europe, it has increased over Asia. To read more about what is driving these trends, read this story.  To learn more about the data used to create these maps, visit this website. 


Areas where PM2.5 concentration has increased between 1998 and 2012 are shown with shades of red. Decreases are shown with shades of blue. Data from van Donkelaar et al.


June Puzzler

June 22nd, 2015 by Adam Voiland


Every month on Earth Matters, we offer a puzzling satellite image. The June 2015 puzzler is above. Your challenge is to use the comments section to tell us what part of the world we are looking at, when the image was acquired, what the image shows, and why the scene is interesting.

How to answer. Your answer can be a few words or several paragraphs. (Try to keep it shorter than 200 words). You might simply tell us what part of the world an image shows. Or you can dig deeper and explain what satellite and instrument produced the image, what spectral bands were used to create it, or what is compelling about some obscure speck in the far corner of an image. If you think something is interesting or noteworthy, tell us about it.

The prize. We can’t offer prize money, but, we can promise you credit and glory (well, maybe just credit). Roughly one week after a puzzler image appears on this blog, we will post an annotated and captioned version as our Image of the Day. In the credits, we’ll acknowledge the person who was first to correctly ID the image. We’ll also recognize people who offer the most interesting tidbits of information about the geological, meteorological, or human processes that have played a role in molding the landscape. Please include your preferred name or alias with your comment. If you work for or attend an institution that you want us to recognize, please mention that as well.

Recent winners. If you’ve won the puzzler in the last few months or work in geospatial imaging, please sit on your hands for at least a day to give others a chance to play.

Releasing Comments. Savvy readers have solved some of our puzzlers after only a few minutes or hours. To give more people a chance to play, we may wait between 24-48 hours before posting the answers we receive in the comment thread.

Good luck!

May Puzzler Answer

June 21st, 2015 by Adam Voiland

Congratulations to reader John Radford for being the first to solve our May 2015 puzzler. As John noted: “It is East Java looking across Surabaya towards Bali and further islands. The numerous lights in the Java Sea must be mostly fishing boats though the cluster dead center may be partly Pulau Kangean lights. The yellowish isolated light about 3/4 of the way up and left of center must be Makassar. The white flash to its left probably is lightning strike onto West Sulawesi proper. The entire landscape is volcanic in origin, Indonesia being the most volcanically active country in the world, at the junction of 4 tectonic plates.” Congratulations also to Claudia for being the first reader who noted it was a photograph taken by an astronaut on the International Space Station. The perspective isn’t exactly the same, but below is a view of the same general area from Google Earth.

Screen Shot 2015-06-22 at 10.56.11 AM

The first thing to know about the new study authored by NOAA scientists about the global warming “slowdown” or “hiatus” over the past decade is that the new analysis gets pretty deep into the details and will mainly be of interest to specialists who study climate science. In fact, for most casual readers, it doesn’t affect the overall story much at all and shouldn’t change what you think about global warming.

As I see it, interest in climate science is a bit like interest in cars. The vast majority of people couldn’t care less about the details of how their car works. They don’t know the difference between a caliper and a camshaft, and they don’t really care to know. They just want the car to run smoothly. Then there is that small but enthusiastic minority — the aficionados and grease monkeys — who not only can name every part of their engine, but who also want to be able to take it apart and fix it without the help of a mechanic. This latest study is really for the grease monkeys of climate science, the folks who know the difference between GISTEMP, HadCRUT4, and can tell you what ERSST stands for without googling it.

For the casual readers among you, here is the extent of what you’ll probably want to know about the study: the NOAA scientists who assess global temperatures have updated their analysis so that it now includes some new data that they think offers a slight improvement. The key thing to understand — for casual readers and data geeks alike — is that the changes are quite subtle. Don’t believe me? Just look at the figure at the top of this page, which shows how the old version of the NOAA analysis compares to the new one. Their newly corrected global temperature trend is the black line. The earlier version of the trend is the red line.

If you look closely, you will see the changes make the temperatures appear slightly warmer in the last decade, and thus make the idea that there has been a slowdown or “hiatus” in warming less credible. Still, that graph also makes it abundantly clear that the changes are quite minor when you look at the bigger picture. As Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, put it in a post on the Real Climate blog: “The ‘selling point’ of the paper is that with the updates to data and corrections, the trend over the recent decade or so is now significantly positive. This is true, but in many ways irrelevant.” As he has pointed out many times (as has this blog), it’s the long term trend that matters more than a handful of years here or there.

Still, there is plenty to dig into about the study for climate data geeks. The NOAA team makes the case that they’ve improved their analysis by making some updates to both the sea surface temperature and land surface temperature datasets that are at the core of the analysis. Specifically, they have included the data from the International Surface Temperature Initiative database, which more than doubles the number of weather stations available for the analysis. They have also updated the sea surface temperature by turning to a new version of the Extended Reconstructed Sea Surface Temperature dataset, which does a better job of correcting for differences in temperature measurements collected by floating buoys versus ships. Buoys are known for getting slightly cooler — and more accurate — readings than ships, but ships were the main way data was collected prior to the 1970s. The NOAA team also took a fresh look at how ship-based measurements taken with wooden buckets as opposed to engine intake thermometers compare, and how the differences might affect the overall analysis.

Not enough detail for you? If you want even more info about the study and want to know how the NOAA team came to its conclusion that there has not been a slowdown in warming over the last decade or so, you will find links to a few places where you can start your reading below the chart.

no slow down in global warming

+ The full study as published in Science:

+ Commentary by Gavin Schmidt:

+ NOAA Press Release about the study:

+ Doug McNeall (of the UK Met Office) commentary about the study:

+Victor Venema (University of Bonn) commentary:

Nature news article about the study:

+Peter Thorne (International Surface Temperature Initiative) commentary:

+ Jay Lawrlmore (NOAA) commentary about the study

+ Washington Post article about the study: