Climate Change and Snowstorms - It's All About the Energy

Snow on rosemary, 2/13/2010, Cary, NC

The story of climate change is the story of energy, in particular, the Earth's balance between incoming and outgoing energy. Our planet's energy equation begins with sunlight. More and more sunlight energy arrives at Earth with each passing day. That sunlight energy warms the ground, bodies of water, plants and animals. Each of those objects in turn radiates its own energy according to its temperature. Since those objects are much cooler than the sun, they radiate energy of a different wavelength than the sun. The sun radiates in the visible wavelengths, but the Earth and everything on it radiates in the infrared wavelengths, which are invisible to our eyes.

Greenhouse gases such as carbon dioxide and methane in our atmosphere are transparent to sunlight just like the nitrogen and oxygen that make up most of our air. However, what makes CO2 and methane effective greenhouse gases is their ability to absorb infrared radiation, something nitrogen and oxygen cannot do. So the greenhouse gases let in sunlight, which warms the Earth, but they do not let infrared radiation escape. Instead, they absorb that infrared radiation and themselves get warmer. As CO2 and methane get warmer, they radiate more infrared radiation themselves, much of it heading back towards the Earth, adding to the warming effects of sunlight.

So the more greenhouse gases reach the atmosphere, the more infrared radiation is absorbed, and the warmer the entire planet becomes. But why would a warmer planet mean more snow or more severe storms?

It's all about the energy. More sunlight coming in and less infrared radiation going out means more energy here. And more energy means higher temperatures, on average. But how can higher temperatures mean more snow?

Because it takes energy to evaporate water. As temperatures rise everywhere, water evaporates faster and faster. More water evaporates from the oceans, from lakes and rivers, even from moist soil. More water even evaporates through the tiny pores covering the leaves of plants growing around the world.

More water evaporation means more total water vapor in the atmosphere, and that inevitably leads to more precipitation. With temperatures above freezing, that precipitation comes down as rain. Drop the temperature below 32°F, and the precipitation comes down as snow or sleet or freezing rain.

Ask a native of Buffalo, New York about the role that water evaporation plays in snowfall. "Lake effect" snow results when water evaporates from a nearby lake - in the case of Buffalo, Lake Erie to the west or Lake Ontario to the north. More water evaporating into the air means more precipitation, and in the winter, even with the greenhouse effect, temperatures can drop below freezing and that precipitation will be frozen. And remember that one inch of rainfall can, if frozen, produce somewhere between 6 and 10 inches of snow.

What is it about a warmer planet that can lead to more severe storms? Storms, with strong winds, heavy precipitation, perhaps even lightning, release a great deal of energy. Where does that energy come from?

Much of the energy in a storm comes from the water vapor in the air within the storm. Remember that it took energy to evaporate that water in the first place. Water vapor carries all the energy it took to evaporate it up into the atmosphere. And as that air rises it cools, and the water vapor cools with it. Eventually the cooling water vapor does not have enough energy to stay a gas, and condenses back into tiny droplets of liquid water, forming clouds. Condensation releases the energy it took to evaporate the water, and that released energy passes to the surrounding air, adding to the strength of the storm.

Global warming driven by a stronger greenhouse effect upsets the energy balance of the planet. More energy evaporates more water. More water vapor makes more precipitation and stronger storms. And in the winter, more precipitation and stronger storms can mean snow and blizzard conditions. Greg Craven, a high school physics teacher, suggested global "weirding" might be a better title than global warming. And that was before the 2010 snowpocalypse hit the mid-Atlantic states.

More on James Hansen's UNC Presentation

Dr. Hansen described the three categories of evidence used to understand climate change. The historical record of temperature and carbon dioxide concentration is first in line, whether that record comes from instruments deployed around the world for which 130-years of data are available, or air trapped in glacial ice, for which data goes back 800,000 years. I would add that the historical record for CO2 and temperature now goes back 20 million years with the publication by Aradhna Tripati of her work with the foraminifera.

The next line of evidence includes current atmospheric and climate conditions, such as temperature data from around the world, glacier conditions in mountains and at the poles, and ocean chemistry.

Third-ranked by Hansen are computer-based climate simulations.

Dr. Hansen went to some length to explain the causes of historical climate variability. In addition to the climate forcings related to the Milankovitch cycles, he mentioned plate tectonic activity. When India was an island continent south of Asia, it was moving north through the Indian Ocean. During this time period, Hansen suggested that large amounts of carbon dioxide were released by volcanic activity triggered by this plate movement. This corresponds to a very warm period on the planet, much warmer than today, when sea levels were considerably higher as there were no large glaciers.

Some mention was also made of the oceans as a sink for atmospheric carbon dioxide, but I missed the reference (2009) and have not been able to find it. The new finding was of carbon measurements down to a depth of 2 km below the ocean's surface, and Hansen was quite excited about it. If any readers out there know of this study, please advise!

James Hansen at UNC Chapel Hill

James Hansen, director of the NASA Goddard Institute for Space Studies, spoke at UNC Chapel Hill earlier this evening. As he put it himself, he is not a communicator, but a scientist who feels compelled to speak out because the gap between what is known by climate scientists and what is understood by a seeming majority of the public is very large and growing.

That he feels so compelled may be the most significant story, but it is not one that I want to tell.

I want to relate the important science story that he told.

He spoke of the inertia in a climate system that encompasses the entire planet. Estimates suggest that we have experienced about half of the warming expected based on the increases in atmospheric carbon dioxide since it was 280 ppm. That means if we immediately reduced our carbon emissions to the point where the atmospheric concentration rose no higher than it is today, we would continue to experience climate change and global warming for some time to come, and about double what has occurred thus far.

Dr. Hansen also spoke about tipping points, moments in time where the climate system may begin to change in ways and at rates over which we will have no control. These tipping points have most to do with positive feedbacks that may begin to operate. There are two big ones according to Hansen. First - melting ice sheets resulting in decreased surface albedo or reflectivity causing more absorption of sunlight and more heating, melting more ice sheets in a spiraling of warming.

Second, the danger of warming oceans allowing methane hydrates on the floor of the shallow areas of the oceans to "thaw" and bubble up to the surface and enter the atmosphere. Methane's greenhouse gas efficiency is more than 20 times that of carbon dioxide. More methane means more heating, meaning warmer oceans, causing the release of more ocean floor methane in a runaway greenhouse scenario. A 2009 story I summarized a while back goes into a little more detail on this feedback loop's scary possibilities.

There were a few other key concepts that will have to wait for a later posting. For now, the take home lesson is that Opa Hansen wants to remind us that global climate change's big losers have either only recently arrived on planet Earth, or have not yet even been born. The decisions we make in the next couple of decades will shape the face of this planet, and strongly influence the quality of life for our grandchildren, great grandchildren, and great great grandchildren.

Sun on Snow

You know how the sunlight shining on fresh snow at a sharp angle can make the snow appear to sparkle? That's what you're looking at in the picture above, believe it or not. If you click on the image to look at a larger version, you should be able to make out different colors, probably a result of diffraction of the sunlight as it passes through tiny ice crystals. Our "snow" actually was sleet, three or four inches of it.

The Tiniest Air Raid Sirens

These little guys are members of the Globigerinoides, planktonic foraminifera that have lived in the surface waters of the ocean for a very long time. The picture of their shell on the left (about the size of a grain of sand) and the living organism on the right, was found at Oceanus, the online magazine of the Woods Hole Oceanographic Institution. The composition of their shells when they lived millions of years ago contains a warning for us today.

But first, what is a foraminifera? Well, living things can be divided into the prokaryotes and the eukaryotes. The prokaryotes include the bacteria and other single-celled organisms without internal membranes, while the more complex eukaryotes have internal membranes around their nucleus and other organelles. The eukaryotes include multicellular plants and animals, the fungi, and a fourth group of single-celled organisms called the protists which are neither animals nor plants. Foraminifera are protists with shells. Their name derives from the tiny holes (foramina) that perforate their shells.

The shells of the foraminifera consist of calcium carbonate, and the changing ratio of boron to calcium in these shells indicates the concentration of carbon dioxide when they formed. The proportion of a particular isotope of oxygen (δ18O) indicates the temperature when they formed. Aradhna Tripati and her colleagues at UCLA, in work published in Science magazine on December 4th, 2009, measured the boron:calcium ratio and δ18O ratio in Globigerinoides shells over a 20 million year span of time, extending all the way back to the Miocene Epoch.

Up until now, the 800,000 year Vostok ice core record in Antarctica held the oldest measurements of atmospheric carbon dioxide and temperature, using air trapped in bubbles in the ice. This ice core record shows carbon dioxide and temperature closely tracking each other over 800,000 years, powerful evidence that CO2 influences climate. But now, Tripati, using the tiny shells of foraminifera dug up in layers of sediment at the bottom of the ocean, extends that correlation between CO2 and temperature 25 times further back in history, to 20 million years before the present.

The significance of this longer and older record of temperature tracking CO2 levels lies with the ice sheets of the Miocene and Late Pliocene. Starting 20 million years ago and continuing for five million years, the globe was warmer, no massive ice sheets covered Greenland and Antarctica, and sea levels may have been 25 to 40 meters higher than today. Atmospheric carbon dioxide during this time increased from around 375 ppm to 425 ppm as climate continued to warm.

Then, 14 million years ago, CO2 levels began a steady decrease over a five million year span of time from over 400 ppm down to 250 ppm. The climate cooled, closely tracking the carbon dioxide decrease, as ice sheets grew and sea levels likely dropped as much as 40 meters.

The take home lesson - massive ice sheets may not survive on planet Earth when atmospheric CO2 levels exceed 350 ppm for an extended period of time. Carbon dioxide reached 350 ppm back in the mid-1980s, peaked at 390 ppm in 2009, continues to increase more than 1.5 ppm every year, and that rate of increase is growing.

Without massive ice sheets, global sea levels can rise as much as 40 meters. That will not likely happen in this century, but the last time CO2 levels rose from 350 ppm to over 400 ppm, it took a million years to do so, and it happened in the Miocene Epoch at least 12 million years ago. We will see CO2 concentrations reach 400 ppm by 2015, just 30 years after CO2 passed 350 ppm.

A sea level rise of just a couple of meters in the next 100 years would constitute a major worldwide catastrophe.

The chemical make-up of ancient foraminifera shells suggests we may be headed to or may have already reached a level of carbon dioxide in our atmosphere that cannot maintain the large ice sheets now covering Greenland and Antarctica, making the Globigerinoides the tiniest air raid sirens in history. Listen to them.

Tree bark

This time of year in a deciduous forest in the northern hemisphere you get to see a great deal of tree bark - gray, brown, flaky, smooth, furrowed and fissured, sometimes with lichen or moss growing on it.

This is the bark on a dogwood tree growing near the Apex Reservoir in Cary, North Carolina. If you click on the image to see it full-sized, you can easily count layers along the descending sides of the fissures in the outer bark or cork. I have not found any confirmation that these layers represent annual growth increments of the outer bark, but if they do, I can count as many as 22 layers in this image.

This outer bark of a tree is a protective layer of dead cells meant to be partially shed as they shield the tree from physical impacts of the weather as well as the grazing of animals from deer, beavers, and birds to insects, and the biological attacks of bacteria, fungi, and viruses. In some trees, this outer bark layer contains materials that resist fire, allowing the tree to survive all but the most intense, canopy fires. A tree can also excrete waste products into the cells of the outer bark.

At or just below the base of the fissures seen in this photograph lies the cork cambium, a layer of actively dividing cells that produce the largely dead outer bark layers. Just beneath the cork cambium lies a layer of living cells called the phelloderm that can serve a variety of roles including photosynthesis, active disease defense, and storage.

Below the phelloderm lies the phloem, the inner bark layer filled with the vascular sieve tubes that carry the sugars produced during photosynthesis in the leaves down to the rest of the tree and its underground roots.

Dig just beneath the phloem and you hit the cambium, the layer of actively dividing cells that produces the thickening or radial growth of the tree trunk. This is the inner end of the bark of the tree, and also the outer beginning of the inside structure of the trunk.

The actively dividing cells of the cambium layer produce not only the bark of the tree, but also the entire inner trunk of the tree. This inner wood, called the xylem, includes a variety of tubes that carry water and dissolved minerals up from the roots to the stems and leaves. The xylem also contains stiff vertical tubes called fibers that support the heavy aboveground weight of the tree.

For an overview of bark found on trees around the world, take a look at ArtSylva's post on the biology of barks. This beautiful site created by photographer Cédric Pollet talks succinctly about the variety of barks, their function for the tree, and their uses for people. And the collection of pictures of bark of all colors and bark found on many different kinds of trees is amazing. If you have not seen a baobab tree, visit this site and find one in Cédric's "Photo Reports" link!

Sounds from a frozen lake!

Once in a while, a great while, down here in the south, it gets cold enough to freeze a lake. I think it's happened once or twice since the big freeze we had in January 2000. A few days ago the lake reservoir behind our house had developed a good bit of ice on its surface. Time to throw a rock across the ice and listen to the lake sing! It's a magical sound. A little web surfing found some recordings of ice "singing" on a frozen lake, and a few attempts to explain this interesting phenomenon. The sound seems to come from the ice itself vibrating like the skin stretched across a drum head. The best recording is Marc Namblard's "Chants of Frozen Lakes"! You can buy his CD, but scroll down a little to listen to some free audio extracts of his recording. Not quite the same as that stone skipping along the ice, but amazing nonetheless. Enjoy!