Tag Archives: Atmospheric sciences

We know pollen helps seed the trees — but what about clouds?

It was the clever headline that caught my attention: “April flowers bring May showers?”

But it was the latest research about pollen from the University of Michigan and Texas A&M that got me digging a little deeper and eventually arriving at the subject of clouds and climate change.

The bottom line is a possibility that pollen from trees and flowers can break apart during a rainstorm. The broken pieces can then float up into the air and seed the clouds for the next rainstorm.

Allison Steiner, associate professor of atmospheric, oceanic and space sciences at U-M, began exploring how pollen might seed the clouds after sweeping a layer of pollen off her front porch one morning and wondering what happens after the pollen drifts into the air.

Atmospheric scientists have never paid much attention to pollen. It is generally believed that pollen grains are too large to seed the clouds. Instead, most attention has been focused on man-made aerosols, such as particles from a coal-fired power plant. High in the atmosphere, the particles can encourage moisture in the air to condense, the initial step in the formation of rain.

But people with allergies may recognize that their symptoms grow worse after a rainstorm when the air begins to dry out. As Steiner explains in an M-I news release:

“When we were looking in the allergy literature we discovered that it’s pretty well known that pollen can break up into these tiny pieces and trigger an allergic response. What we found is when pollen gets wet, it can rupture very easily in seconds or minutes and make lots of smaller particles that can act as cloud condensation nuclei, or collectors for water.”

In a laboratory at Texas A&M, Sarah Brooks, a professor in atmospheric sciences, soaked six different kinds of pollen in water, then sprayed the moist fragments into a cloud-making chamber. Brooks and her colleagues found that three fragment sizes — 50, 100 and 200 nanometers — quickly collected water vapor to form cloud droplets, which are 10 times bigger than the particles. (It takes about 6 million nanometers to equal a quarter of an inch, so we’re talking about very small particles.) Brooks noted in a Texas A&M news release:

“Scientists are just beginning to identify the types of biological aerosols which are important for cloud formation. Our results identify pollen as a major contributor to cloud formation. Specifically, our results suggest that increased pollen could lead to the formation of thicker clouds and longer cloud lifetimes.”

The effect of cloud formation on global warming may be the most important mystery in climate science today, according to Jasper Kirby, a particle physicist who is leading a team of atmospheric scientists from 15 European and U.S. institutions. Consequently, the effect of aerosols on cloud formation must be equally important.

Clouds are known to cool the planet by reflecting sunlight back out to space, but they can also contain heat at night, so cloud formation plays a critical role in determining the rate of global warming. To better predict global warming, one has to better understand when and how clouds are formed at a “very fundamental level,” Kirby told reporter Rae Ellen Bichell in “Yale Environment 360.” Kirby added:

“By fundamental, I mean we have to understand what the gases are, the vapors, that are responsible for forming these little particles. And secondly, we have to understand exactly how quickly they react with each other and how they form the aerosol particles which … constitute the seeds for cloud droplets. And this process is responsible for half the cloud droplets in the atmosphere. It’s a very, very important process, but it’s very poorly understood.”

In the upper atmosphere, aerosols can directly reflect sunlight back into space. These include man-made aerosols from industrial pollution as well as natural aerosols, such as volcanic eruptions and desert dust and now possibly pollen. Check out NASA’s webpage on “Atmospheric Aerosols.”

Steiner, who is doing the pollen experiments, said understanding natural aerosols is critical to understanding climate change:

“What happens in clouds is one of the big uncertainties in climate models right now. One of the things we’re trying to understand is how do natural aerosols influence cloud cover and precipitation under present day and future climate.

“It’s possible that when trees emit pollen, that makes clouds, which in turn makes rain and that feeds back into the trees and can influence the whole growth cycle of the plant.”

For people more interested in the allergy aspects of this story, I found a website called pollen.com, which identifies a variety of ways that weather can affect pollen and thus allergies:

  1. A mild winter can lead to early plant growth and an early allergy season,
  2. A late freeze can delay pollen production in trees, reducing the risk of an allergic reaction,
  3. Dry, windy weather increases the spread of pollen and worsens allergy symptoms,
  4. Rain can wash pollen out of the air, reducing the risk of exposure to pollen, but
  5. Rain can also increase the growth of plants, especially grasses, increasing the pollen levels.

For a research report about how rain can break up pollen into smaller particles to trigger allergies, check out “Thunderstorm-associated asthma in Atlanta, Georgia” by Andrew Grundstein et al.

Earth gets hot in 2014, breaks record for average temperature

UPDATE, Jan. 20, 2015
Some people apparently are skeptical about whether 2014 was actually the warmest on record. They cite probabilities provided by government researchers to support their skepticism. But at least some skeptics seem confused about the meaning of this statistical uncertainty.

Andrew Freedman of Mashable tackles the subject in a straightforward way. But the best point in his piece comes in the final paragraph:

At the end of the day, the discussion about a single calendar year obscures the more important long-term trend of warming air temperatures, warming and acidifying oceans along with melting ice sheets, all of which are hallmarks of manmade global warming. Including 2014, 13 of the top 15 warmest years have all occurred since 2000.


Last year turns out to be the hottest year on record for the Earth’s surface, according to climate researchers who analyzed average temperatures across the globe.

The year 2014 adds yet another dramatic page to the record book, which now shows that the 10 warmest years since 1880 have occurred since the year 2000 — with the exception of the record year of 1998, which now stands as the fourth warmest on record.

The data were released this morning, with additional information provided in a telephone conference call with scientists from NOAA — the National Oceanic and Atmospheric Administration — and NASA — the National Aeronautics and Space Administration. The two agencies conducted independent analyses of their data, coming to the same conclusion about the record year of 2014.

Across the Earth, the average temperature in 2014 was 1.24 degrees Fahrenheit above the annual average of 57.0 degrees F, with records going back to 1880. That breaks the previous records of 2005 and 2010 by 0.07 degrees F. It’s also the 38th consecutive year that the annual global temperature was above average.

Since 1880, the Earth’s average surface temperature has warmed by about 1.4 degrees Fahrenheit, mostly driven by an increase in carbon dioxide and other greenhouse gases released into the atmosphere, the researchers said. Most of the warming has come since the 1980s.

Gavin Schmidt, director of NASA’s Goddard Institute of Space Studies, made this comment in a prepared statement:

“This is the latest in a series of warm years, in a series of warm decades. While the ranking of individual years can be affected by chaotic weather patterns, the long-term trends are attributable to drivers of climate change that right now are dominated by human emissions of greenhouse gases.”

Although some skeptics have raised questions about whether global warming has been occurring in recent years, Schmidt said any short-term pause does not change the overall trend. In fact, the temperature rise seen for the past year fits perfectly onto a graph of the decades-long trend line for temperature rise.

temp graph

Ocean conditions such as El Nino or La Nina can affect temperatures year-to-year, Schmidt said. Since these phenomena can cool or warm the tropical Pacific, they probably played a role in temporarily “flattening” the long-term warming trend over the past 15 years, he added, but last year’s record-breaking temperatures occurred during a “neutral” El Nino year.

This past year was the first time since 1990 that the global heat record was broken in the absence of El Nino conditions during the year. If El Nino conditions are present at the end of 2015, the researchers said the chances are high that the record will be broken again this year.

As I mentioned in yesterday’s post in Water Ways, strong regional differences were seen last year in the contiguous United States, with several western states experiencing record highs while the Midwest suffered through an abnormally cold winter. Other cold spots can be seen on the global map, but the hot spots more than balanced them out to break the heat record.

global temps

Much of the record warmth of the Earth can be attributed to record heat accumulated across the oceans. The average ocean temperature in 2014 was 1.03 degrees higher than the longterm average of 60.9 degrees, breaking previous records set in 1998 and 2003.

Record months for ocean temperatures were seen from May through November, with January through April each among the all-time top seven, while December was the third warmest December on record. The all-time monthly record was broken in June of last year, then broken again in August and again in September. Such sustained warmth in the ocean has not been seen since 1997-98 — during a strong El Nino.

On the land surface, the average temperature was 1.8 degrees higher than the long-term average of 47.3 degrees F, or the fourth highest average land temperature on record.

Europe is expected to report that 2014 was the warmest year in at least 500 years, according to information from the World Meteorological Organization. Last year surpasses the previous record set in 2007. Much of that warmth can be attributed to the second-warmest winter on record, followed by a record-warm spring.

According to the WMO report, 19 European countries have reported or are expected to report that last year was their hottest year on record. They Austria, Belgium, Croatia, the Czech Republic, Denmark, France, Germany, Hungary, Iceland, Italy, Luxembourg, The Netherlands, Norway, Poland, Serbia, Slovakia, Slovenia, Sweden, and the United Kingdom.

Around the world, precipitation was near average for 2014, the third year that near-average precipitation was measured for land-based stations.

The 10 warmest years on record, in order:

1. 2014, 1.24 degrees above average
2 (tie). 2010, 1.17 degrees above average
2 (tie). 2005, 1.17 degrees above average
4. 1998, 1.13 degrees above average
5 (tie). 2013, 1.12 degrees above average
5 (tie). 2003, 1.12 degrees above average
7. 2002, 1.10 degrees above average
8. 2006, 1.08 degrees above average
9 (tie). 2009, 1.06 degrees above average
9 (tie). 2007, 1.06 degrees above average

For further information, check out:

Global Analysis — Annual 2014 from NOAA, and

GISS Surface Temperature Analysis from NASA.

Computer model shows colorful swirls as winds blow carbon dioxide

An ultra-high-resolution computer model ties weather into greenhouse gas emissions, and the resulting animation shows whirling and shifting plumes of carbon dioxide and carbon monoxide.

Ultimately, the greenhouse gases disperse into the atmosphere, increasing concentrations across the globe and contributing to global warming. It’s almost too complex to comprehend, but it is a fascinating process.

As you can see from the video, carbon dioxide levels are more significant in the Northern Hemisphere, where the emissions are out of phase with the Southern Hemisphere. That’s because the seasons are opposite, with the maximum growth of vegetation taking place at different times.

The reds and purples are the highest concentrations of carbon dioxide. The dark grays denote the highest levels of carbon monoxide, caused mainly by large forest fires.

Bill Putman, of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said it a prepared statement:

“While the presence of carbon dioxide has dramatic global consequences, it’s fascinating to see how local emission sources and weather systems produce gradients of its concentration on a very regional scale. Simulations like this, combined with data from observations, will help improve our understanding of both human emissions of carbon dioxide and natural fluxes across the globe.”

The animation was produced with data from measurements of atmospheric conditions plus the emission of greenhouse gases, both natural and man-made. The simulation, called “Nature Run,” covers a period May 2005 to June 2007. Engineers can use the model, called GEOS-5, to test satellite observations.

In July, NASA launched the Orbiting Carbon Observatory-2 (OCO-2) satellite to make global, space-based carbon observations. The additional data will add to Earth-based measurements. See also OCO-2 Mission Overview.

According to studies, last spring was the first time in modern history that carbon dioxide levels reached 400 parts per million across most of the Northern Hemisphere. Concentrations are continuing to rise, mainly from the burning of fossil fuels. Levels were about 270 ppm before the Industrial Revolution.

The GEOS-5 computer model is being used in tests known as Observing System Simulation Experiments (OSSE), which can help satellite observations tie into weather and climate forecasts.

Said Putnam:

“While researchers working on OSSEs have had to rely on regional models to provide such high-resolution Nature Run simulations in the past, this global simulation now provides a new source of experimentation in a comprehensive global context. This will provide critical value for the design of Earth-orbiting satellite instruments.”

For more detailed views involving various parts of the world, see “A Closer Look at Carbon Dioxide” on NASA’s website for “Orbiting Carbon Observatory 2.” For information about modeling, visit the website of the Global Modeling and Assimilation Office.