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An artist's rendering of the asteroid impact that took place 65 million years ago and likely killed off nearly every large vertebrate species on the planet, including, many think, the dinosaurs. Don Davis/NASA

An important finding was reported last week in the same issue of Science as the new studies of Ardipithecus, and unfortunately, overshadowed by the news of the 4-million-year-old hominid.  This finding may turn out to be even more important because it relates not to the evolution of a single species, but to the recovery of life in general on Earth following one of the greatest catastrophes ever.

I’m referring to a paper by Julio Sepúlveda and others called “Rapid Resurgence of Marine Productivity After the Cretaceous-Paleogene Mass Extinction.”

Sepúlveda and colleagues examined marine sediments in Denmark that date to the period following the K-T mass extinction event. That event consisted of an impact on the Earth of a large asteroid 65 million years ago and the subsequent extinction of many species including all the dinosaurs. It is thought that there was a huge drop in the biological activity in the oceans after the event because the sun was largely blocked out, reducing photosynthesis in ocean-living algae. Without sun, the algae would have died off, and without algae, which are at the base of the oceanic food chain, other life forms in the ocean would die off or become very rare. The more widely accepted reconstructions of what happened indicate that this oceanic die-off did indeed happen, and that it took up to three million years for the ecosystems of the open ocean to recover from this impact. (Near-shore ecosystems have been thought to recover much more quickly.) The relatively lifeless post-impact open ocean is sometimes referred to as the “Stangelove ocean” in reference to the character in the apocalyptic movie “Dr. Strangelove.”

That previous research, however, was based on the examination of fossils of marine organisms including algae that leave an easily fossilized “skeleton” of silica, which indeed are sparse for a very long time after the impact. However, it is possible that certain types of organisms that do not leave behind fossils, such as cynobacteria, were abundant and would remain undetected in the fossil record.

The paper by Sepúlveda and colleagues used a different kind of evidence to look for open ocean biological activity and found it, in abundance, possibly within a century after the impact. If this proves to be true, then the darkening of the sky following the impact must have been fairly short term, and the observed long-term disruption of the ocean’s ecosystems must have a different explanation.

“Primary productivity came back quickly, at least in the environment we were studying,” according to Roger Summons, one of the paper’s authors.  “The atmosphere must have cleared up rapidly.  People will have to rethink the recovery of the ecosystems. It can’t be just [because of] the lack of food supply.”

The method this research team used was to look for isotopically distinct materials in the ocean sediments they examined, as well as molecules that could only have been formed by living things.

The sediments they looked in consist of a 37-centimeter-thick layer of clay in Denmark. Within this clay, which was deposited in relatively shallow near-shore environments, are hydrocarbon molecules produced by living organisms that are reasonably well preserved from 65 million years ago. These molecules indicate the existence of extensive open oceanic photosynthesis that would not have been possible under the “Strangelove ocean” model.

The way the analysis works can be understood this way: The ocean has a lot of dissolved carbon in it. This carbon exists in the form of more than one isotope. An isotope is a version of an element that is only a tiny bit different in its nuclear composition, and most elements lighter than Uranium have multiple non-radioactive isotopes. If there was no life in the ocean, the carbon would reach a certain equilibrium with respect to the proportion of each isotope, so sediments that included carbon would have a predictable ratio of these isotopes. (Note:  This has nothing to do with radiocarbon dating.  See this blog post for more on the potential confusion about that issue.)

Living forms use carbon, but when carbon is taken from the surrounding environment certain isotopes are incorporated into biological tissue more readily than others. Which isotopes are used and in what way by biological systems, and the exact reason for this, is complex and far beyond the scope of a mere blog post! Suffice it to say that when a geochemist looks at a sample of carbon, using very sensitive instruments, she can tell if this carbon has come from a non-biological system vs. a biological system. Beyond this, it is even possible to tell what kind of biological system is represented.

Sepúlveda’s team was able to tell that the carbon in these post-impact sediments could only have been assembled into these hydrocarbons (and other compounds) in a functioning open ocean ecosystem with plenty of algae photosynthesizing away at a pretty good clip. Since these sediments were deposited right after the impact, the “Strangelove” ocean theory, with a vast lifeless sea, is highly unlikely.

Greg Laden is guest-blogging this week while Sarah is on vacation. You can find his regular blog at Scienceblogs.com and Quiche Moraine.

You may know that much of the climate change on earth over the last two million years–the coming and going of ice ages–is caused by the “orbital geometry” of the planet. The amount of planetary tilt and the time of year the tilt occurs change over time. When the Northern Hemisphere is less tilted towards the sun on June 21st, and at the same time the Earth is as far from the sun in its elliptical orbit as it ever gets, ice age conditions prevail. This makes ice ages on Earth pretty regular, cyclic, events.

You also may know that a big chunk of Earth’s water is frozen into the ice caps.

You also may know that the history of Earth climate is preserved, in part, in changes in the ice in those ice caps.

Well, same for Mars!

Images from the Shallow Radar instrument on NASA's Mars Reconnaissance Orbiter. Pane "a" is a "radargram" cross section, showing distinct layers.

Previously developed climate models suggested that the last 300,000 years of Martian history experienced low-level swings in climate, while the prior 600,000 years experienced more severe swings, owing to differences in the tilt of the planet. Most of the water we know about on Mars is in the Martian polar caps. And now, we can see, using radar, evidence of climate change reflected in that ice. From NASA:

New, three-dimensional imaging of Martian north-polar ice layers by a radar instrument on NASA’s Mars Reconnaissance Orbiter is consistent with theoretical models of Martian climate swings during the past few million years.

Alignment of the layering patterns with the modeled climate cycles provides insight about how the layers accumulated. These ice-rich, layered deposits cover an area one-third larger than Texas and form a stack up to 2 kilometers (1.2 miles) thick atop a basal deposit with additional ice.

“Contrast in electrical properties between layers is what provides the reflectivity we observe with the radar,” said Nathaniel Putzig…, a member of the science team for the Shallow Radar instrument on the orbiter. “The pattern of reflectivity tells us about the pattern of material variations within the layers.”

Essentially, the radar detects different amounts and/or kinds of dirt, and the ice is dirty in different ways. These vastly different climate periods (of more vs. less severe oscillation in climate change) probably leave behind different amounts of dirt in the ice. The radar can penetrate the ice and “see” these differences, with one period having more dirt than another.

There are two distinct models for how the dirt gets concentrated in the ice enough to be distinguished by the radar. One is that ice evaporates away more during some periods than others, leaving behind more dirt when the ice disappears, like the dirty snow during the late winter in northern cities. The other model simply has more dust in the atmosphere, and thus more dust falling on the ice, during certain periods. The present study supports the later model (more dust = dirtier ice). The radar reflectivity signal observed in this study is probably too coarse to link specific features of the signals with specific Martian “ice ages” so far.

“The radar has been giving us spectacular results,” said Jeffrey Plaut of NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a co-author of the paper. “We have mapped continuous underground layers in three dimensions across a vast area.”

Read more about this study.

The other images are different views of the polar cap using the radar images, and are explained in great detail on NASA’s site.

Close-up of a sunspot (Credit: Vacuum Tower Telescope, NSO, NOAO)

One of the more persistent climate change myths is that any warming we’ve been experiencing here on Earth is because of sunspots, not increasing amounts of greenhouse gases in our atmosphere. Of course, the Sun is an important factor in climate, and changes in solar output are suspected to be behind large climate events such as the Little Ice Age. But how the Sun can have an effect that big has been a bit of a mystery for scientists; changes in the amount of energy put out by the Sun are not enough on their own to account for the magnitude of the effects on Earth.

In a new study in Science, Gerald Meehl of the National Center for Atmospheric Research and colleagues contend that two mechanisms work together to produce the changes seen when the sunspot cycle hits its peak and there is a small increase in the amount of ultraviolet radiation produced by the Sun.

With the “bottom up” mechanism, the extra solar energy results in more water being evaporated from the ocean, causing fewer clouds to form in the subtropics and more solar energy to reach the ocean, creating a feedback loop.

With the “top down” mechanism, the extra solar energy causes changes in the upper atmosphere that result in changes in precipitation in the tropics.

The two mechanisms reinforce each other by boosting the rising of tropical air that is driven by evaporation, Meehl [explained to Science]. “That’s the key commonality,” he says. “That amplifies things.”

The result is an equatorial eastern Pacific that is cooler and drier than usual, similar to a La Nina event, and the peak of the sunspot cycle could thus work to enhance a La Nina event or dampen El Nino. So variations in solar activity can drive changes in the weather. But that doesn’t mean solar activity is to blame for global warming, as Meehl and his colleagues note:

This response…cannot be used to explain recent global warming because the 11-year solar cycle has not shown a measurable trend over the past 30 years.

Climate change skeptics—you’ve been warned.

Venice flooding may not end with floodgates (courtesy of flickr user gwenael.piaser)

Yes, I’m being a bit melodramatic in the headline, but every time that I read about the bad things that are predicted to happen—or already are happening—due to climate change, I worry. (And if you’re about to leave a comment saying that climate change isn’t real, please read this post about weather and climate first.) In the last month, I’ve come across half a dozen stories that give me pause:

The people of Venice thought that they would have their flooding problem fixed with a new floodgate system, but they might have breathed their sighs of relief too soon. A new study in the Journal of Climate Dynamics predicts that by the end of the century, the city’s subsidence (i.e., sinking) combined with rising sea levels from climate change could increase the number of floods from four per year to between 20 and 250 per year. The floodgates alone may not be enough to protect the city, and even if they are, closing off the city from the sea would mean that pollution and untreated sewage would not be able to be flushed out as frequently. Ew.

City dwellers here in the United States have reason to worry, too. A new report from Physicians for Social Responsibility and the National Wildlife Federation warns that rising summer temperatures in urban areas (which will mean more frequent heat waves) could be particularly dangerous to children, the elderly and African-Americans, who are more likely to live in urban areas and be poor. Extreme heat can not only lead to death through heat stroke, but it also may exacerbate other problems, such as asthma.

The situation isn’t any better down on the farm. Wolfram Schlenker of Columbia University and Michael Roberts of North Carolina State University in Raleigh looked at weather patterns and crop yields from 1950 to 2005 to predict how warmer temperatures might affect corn, cotton and soybeans. They found that the amount of time spent about 84 degrees F correlated with drops in yield. Based on current climate models, corn yields could decrease by 82 percent by the end of the century if greenhouse gas emissions continue apace.

Then there’s the New York Times article about the threat of climate change to national security. “The changing global climate will pose profound strategic challenges to the United States in coming decades, raising the prospect of military intervention to deal with the effects of violent storms, drought, mass migration and pandemics, military and intelligence analysts say.” Eek.

Climate change and polar bears don't mix well (courtesy of flickr user Just Being Myself)

Those poor bears. A new analysis in the Journal of Zoology of polar bear skulls collected from 1892 to 2002 finds that the bears have shrunk by about nine percent over that time. The researchers say that stress from increased pollution and disappearing sea ice is the likely cause. As the sea ice shrinks, the bears have to spend more and more time searching for food.

And finally, the weirdest of possible outcomes from climate change: the tilt of the Earth could shift. As we learned in school, the Earth is tilted 23.5 degrees from vertical; this is why we have seasons. But that tilt can change over time. As ice melts, warmer water expands and water in general moves from one place to another—as is expected with climate change—the motion of that water an effect on the planet’s tilt. It’s a small effect—only about 1.5 centimeters per year—but combine that with the knowledge that the redistribution of the water’s mass will have an effect on the Earth’s spin. I find it a little scary that humans, through fossil fuels, can affect the world in such a way.

The Incan walled complex of Sacsayhuamán near Cuzco, Peru (courtesy of flickr user Altamar)

In 1532, when the Incas first met a European, their empire stretched from what is now northern Ecuador to central Chile. The largest empire of the Americas numbered more than eight million people. But the Incas didn’t exist until about A.D. 1100. Before than, the Wari and Tiwanauku occupied the central Andes.

Archaeologists suspected a worsening environment led to the disappearance of the Wari and Tiwanauku. But what about the Incas’ rise? To get a better idea of the factors that shaped these early South American civilizations, a group of French-led scientists examined a 26-foot-long mud core taken from a Peruvian lake. Their analysis appears in the journal Climate of the Past.

The mud core trapped pollen, seeds, charcoal and other bits in layers for 4,000 years. By analyzing the contents of this debris, the archaeologists developed a picture of the region’s changing climate, particularly during the time of the Wari, Tiwanauku and Incas.

For the 3000 years before A.D. 1000, the region had cool temperatures. But around 880, a drought began and lasted for at least 100 years. This corresponds with the declines of the Wari and Tiwanauku.

Then around A.D. 1150, the climate began to warm by several degrees. That would have extended the land that could be planted by about 300 yards in elevation. In addition, melting glaciers could have provided more water for irrigation.

With all the extra land to be cultivated, the Incas could have had large surpluses of food (in fact, when the Spanish arrived, they found a 10-year supply of food in the Incan warehouses). More food would have meant more freedom to build roads and monuments and create an army big enough to conquer neighbors.

Of course, all of this is speculation, and more work is needed to match up the archaeological and climate records. As archaeologist Warren Church of Columbus State University in Georgia told the Los Angeles Times: “It is important to remember that climates do not make empires. People do.”

The temperature doesn’t tell you much about climate change (courtesy of flickr user jo3design)

Seattle and the Pacific Northwest are frying under a heat wave this summer. In New York, it’s so cool that the New York Times has called it “the summer that isn’t.” And Texas is suffering under the most severe drought since the 1950s.

What does this all mean for climate change?

Absolutely nothing.

Every time we write about climate change, someone writes in saying that they are shocked that Smithsonian would perpetuate such a myth. Don’t we know about the record cold/snow/rain/etc. in Minnesota/North Carolina/Utah/etc.? Obviously, there are some people who do not understand the difference between weather and climate. Let’s start with the dictionary definitions:

Weather: the state of the atmosphere with respect to wind, temperature, cloudiness, moisture, pressure, etc.

Climate: the composite or generally prevailing weather conditions of a region, as temperature, air pressure, humidity, precipitation, sunshine, cloudiness, and winds, throughout the year, averaged over a series of years.

In short, weather is a data point. Climate is a collection of data.

You can think of it like the economy. I can tell you that the Dow is up 112.61 as I write this, at 9,284.22. This is the weather (partly sunny, 84 F). But it doesn’t tell you anything useful about the economy as the whole (like the weather conditions don’t tell you anything useful about climate). A graph of the Dow over the last year, showing a terrifying decline followed by a steady rise, begins to tell the story of the last year. But to get a true picture of the economy, we’ll need to look at lots of other bits of data, like consumer confidence, unemployment rates and durable goods orders. It’s complicated, messy and hard to understand. That’s climate.

Now, if you make changes to the country’s economic situation, for example, by raising taxes, that is going to have some effect on the economy as a whole. Economists will crunch the numbers and come out with predictions. They won’t all be the same, but they will probably trend toward some particular end.

Adding carbon dioxide to the atmosphere is akin to raising taxes. We’ve changed the climate situation. And while these climate models—which are far simpler than economic models and more certain—may not agree on the specifics, the general trend is that temperatures are going to rise.

And they have been rising. And more than that, we can already see the effects of that rise. Just read the magazine: We’ve featured melting glaciers, melting permafrost and changes in plant and animal distributions in the Andes and, closer to home, the Northeast, to name a few.

So please don’t write to us to say that we’re neglecting the latest weather superlative. We’re not. We just have our eyes on the bigger picture—climate.

When my daughter was small, I used to take her to the American Museum of Natural History in New York City. There, I would explain why the dinosaurs disappeared and how mankind evolved from our primitive forebears. She seemed rapt. But a few weeks ago, after hearing me on the radio discuss a new book about Charles Darwin, my daughter, now 25, suggested that we reverse roles—she’d take me to the museum. She said my understanding of Darwinism needed some fine-tuning.

Thus begins Joe Queenan’s excellent Last Page essay, Darwin for Dads, in Smithsonian magazine’s August issue, now online. It’s another month packed with science. Here are the highlights:

August 2009 Smithsonian

River of Riches: The Cahaba, an unsung Alabama waterway, turns out to be one of the most biologically diverse places in the nation

Finding Herod’s Tomb: Archaeologists and treasure hunters had long scoured a mountain outside Jerusalem for the biblical king’s resting place. Ehud Netzer is certain he has found it—mere steps from where he stood decades before

Mad About Shells: For centuries, scientists, collectors and thieves risked life, limb and fortune to gather the rarest specimens. Now interest is turning to the medical potential of the animals within

Galileo’s Vision: Four hundred years ago, the Italian scientist looked into space and changed our view of the universe. A new exhibit brings one of his telescopes to the U.S. for the first time

Blue Sky Thinking: How an unlikely mix of environmentalists and free-market conservatives hammered out the strategy known as cap-and-trade

Evolution’s Big Bang: A storied trove of fossils from Canada’s Burgess Shale is yielding new clues to an explosion of life on earth

Cracking the Code: Smithsonian scientists barcode every plant on a small island near Washington, D.C.

Wild Things: Snakes, Siberian jays, laughing apes, guilty-looking dogs and a new plant structure—snow roots

Click on the graphic to see what you can expect from climate change.

What kind of changes can you expect as carbon dioxide levels in the atmosphere rise? Here are some highlights of changes based on geographic region, from Global Climate Change Impacts in the United States, a new report from the U.S. Global Change Research Program:

Northeast: Shorter winters with less snow and more rain; longer summers, more frequent extreme heat waves and declining air quality, especially in cities; more frequent short-term (one- to three-month) droughts; severe flooding from sea level rise and heavy downpours; lobster fisheries shift North; declines in dairy, fruit and maple syrup production.

Southeast: Higher summer temperatures will lead to more human illness, road buckling, a decline in forest growth and a decline in livestock production; decreased water availability, leading to increased conflict over water issues (like in Atlanta in 2007); rising sea levels, more intense hurricanes and bigger storm surges could threaten a large portion of the coast.

Midwest: Reduced public health in the summers due to more heat waves, reduced air quality and more insect and waterborne diseases; declining water levels in the Great Lakes, which will affect shipping, recreation and tourism; more precipitation in the winter and spring, with more heavy downpours; precipitation changes in the summer will bring both more droughts and more floods; managing agriculture and forests will be difficult in a time of rapidly changing climate patterns.

Great Plains: More frequent extreme events, including heat waves and droughts; increases in droughts, evaporation and temperature could exacerbate water management issues, particularly for agriculture and ranching; alterations to unique habitats, such as prairie potholes, could affect native plants and animals.

Southwest: Increasing water scarcity to lead to more conflict between states; higher temperatures, drought, wildfires and invasive species change the landscape of this region; more frequent flooding puts people at risk; tourism and recreation declines.

Northwest: A declining snowpack leads to lower summer streamflows and less hydroelectric output; salmon threatened by the lower streamflows and higher water temperatures; more wildfires and insects and shifts in species threaten both ecosystems and the forest industry.

Alaska: Hotter, drier summers; more wildfires and insect problems; more lake evaporation, which could affect native bird populations and Native peoples who depend on hunting and fishing; thawing permafrost undermines infrastructure, including roads and buildings; loss of sea ice leads to more coastal storms, which threaten villages and fishing fleets; possible declines in key fisheries.

Hawaii, Puerto Rico and other islands: Less freshwater availability; sea level rise and more intense storms threaten island communities; changes to coastal and marine ecosystems will affect fisheries and tourism.