The joker who brought climate science out of the cold

Wally Broecker, when he registered for the Columbia University geology department in 1953. Credit: Department of Earth and Environmental Engineering Archives, Columbia University

Wally Broecker, when he registered for the Columbia University geology department in 1953. Credit: Department of Earth and Environmental Engineering Archives, Columbia University

In Los Angeles on September 1 1955, the day temperatures reached a new record of 43°C, Wally Broecker stood, sweating, giving the first scientific talk of his life. He could scarcely have guessed where the new method he was telling an audience of sleepy archaeologists about, called radiocarbon dating, would send him. But thanks in part to its messages from history he would help spawn the phrase ‘global warming’ and warn of its effects, which have today pushed temperatures even higher.

Wally grew up and started college on the outskirts of Chicago, Illinois, good at maths, but largely uninterested in science. But college-mate Paul Gast steered his career sciencewards by helping get him a summer job at the new Lamont Geological Observatory that Paul had recently started working at. On June 15, 1952 Wally and pregnant wife Grace drove 800 miles to the Palisades, New York mansion Columbia University had inherited, and set up the observatory in. There, in the basement, Wally worked in and soon practically ran Laurence Kulp’s radiocarbon lab. Rather than lose him at the end of the summer Laurence organised for Wally to transfer to Columbia and stay working at Lamont, where he has remained ever since.

Taking advantage of the slow decay of a rare, radioactive form of carbon – carbon-14 – radiocarbon dating was in its infancy. The balance between carbon-14 and the usual form, carbon-12, is quite steady in CO2 in the air, and also in living plants that take up the gas as they grow. But when plants die, the carbon-14 they contain slowly decays to nitrogen. Measuring the ratio between the two forms of carbon, scientists can tell when the plants had died. But in 1952, Laurence’s lab was getting inconsistent readings, with carbon-14 counts sometimes coming out too high, even after Wally had fixed a problem with the equipment. Then Wally realised the problem came from outside the lab. The extra counts were coming from nuclear tests that had recently started over Nevada.

Read the rest of this entry »

Advertisements

Projected warming set to exceed civilisation’s experience

Oregon State University's Shaun Marcott has built a climate record reaching back 11,300 years, showing that today's temperatures are warmer than at least 70% of that period. Credit: Shaun Marcott

Oregon State University’s Shaun Marcott has built a climate record reaching back 11,300 years, showing that today’s temperatures are warmer than at least 70% of that period. Credit: Shaun Marcott

The world is headed for average surface temperatures warmer than it has seen in at least 11,300 years. That’s one conclusion US researchers have reached after bringing together 73 studies of ancient climate from across the world into a single global record. Their work supports previous records for the past 2,000 years built mainly from tree ring data, explained Shaun Marcott from Oregon State University, and gives a much broader view.

“We can put today’s global temperature into context against the entire Holocene period,” Shaun told me. “That’s when human civilisation was born, developed and progressed to today.” Modern temperatures are higher than in around three-quarters of that period, which reaches back to the end of the last ice age. And their comparison against forecasts for 2100 made in models used by the Intergovernmental Panel on Climate Change (IPCC) is even starker. “If those scenarios come to fruition, we’ll be well outside anything human civilisation has seen,” Shaun warned. “We won’t have even have been close.”

Knowing climate’s history helps understand its present, and so researchers have puzzled out temperatures on the Earth’s surface from proxy, or indirect, records for the last 2,000 years. In particular, bringing together measurements from tree rings, ice and coral has showed a sharp recent temperature rise often referred to as the ‘hockey stick’. Meanwhile, studies scattered across the world had reached back across the 11,300 years since the beginning of the Holocene. But they can be influenced by regional effects, and no one had pieced them into a global view that would overcome that. Read the rest of this entry »

Global view answers ice age CO2 puzzle

Paleoclimate researcher Jeremy Shakun. Credit: Harvard University

Paleoclimate researcher Jeremy Shakun. Credit: Harvard University

Previous data suggesting that the world started warming out of the last ice age before CO2 levels in the atmosphere started rising don’t show the full picture. That’s according to US, French and Chinese scientists who have added to those Antarctic measurements with more taken from 80 locations across the globe. Harvard University’s Jeremy Shakun and colleagues show the greenhouse gas rises before temperature, supporting the case that CO2 drove climate change then, as it is now. “This provides a very tangible example of what rising CO2 can mean for the climate over the long term,” Jeremy said.

In the 1980s, researchers began building the history of CO2 in the atmosphere from cylinders of ice drilled from the Antarctic. Bubbles in the ice contain air from the time they formed, which researchers can measure. They can also figure out how old the ice holding the bubbles is from how deep it is in the core. And finally they can also work out temperature from the amount of the different forms, known as isotopes, of elements like hydrogen, carbon and oxygen in the ice. That’s because the temperature at which the snow that eventually became the ice formed affects how much of each it contains. And because some isotopes are radioactive and decay to a more stable isotope with time, studying them gives scientists another way to check the ice’s age.

The 800,000 year record of atmospheric CO2 from Antarctic ice cores, and a reconstruction of temperature based on hydrogen isotopes in the ice. The current CO2 concentration of 392 parts per million (ppm) is shown by the blue star. Credit: Jeremy Shakun/Harvard University

The 800,000 year record of atmospheric CO2 from Antarctic ice cores, and a reconstruction of temperature based on hydrogen isotopes in the ice. The current CO2 concentration of 392 parts per million (ppm) is shown by the blue star. Credit: Jeremy Shakun/Harvard University

Such methods show temperature and CO2 levels rising and falling together for 800,000 years, Jeremy told journalists over the phone on Tuesday. “The question is: Which is the cause and which is the effect?” he asked. “If you look up close you see temperature changed before CO2 did. This is something the global warming skeptics have jumped on to say, ‘Obviously CO2 doesn’t cause warming because it came after the warming in these records’. But these ice cores only tell you about temperatures in Antarctica. For the same reason that you don’t look at just one thermometer from London or New York to prove or disprove global warming, you don’t want to look at just one spot in the map to reconstruct the past either.” Read the rest of this entry »

Climate models pass prehistoric test

Microfossils used in mid-Pliocene paleoclimate research. Clockwise from top left: ostracode, planktic foraminifer, diatom, benthic foraminifer, and pollen grain. One way scientists reconstruct past climate is by comparing the spatial distribution of these microfossils with the distribution of their relatives living in today's climate. Foraminifera and ostracoda carry additional climate information in their elemental ratios; for example, the ratio of magnesium to calcium varies with ocean-water temperature. Credit: US Geological Survey

Microfossils used in mid-Pliocene paleoclimate research. Clockwise from top left: ostracode, planktic foraminifer, diatom, benthic foraminifer, and pollen grain. One way scientists reconstruct past climate is by comparing the spatial distribution of these microfossils with the distribution of their relatives living in today's climate. Foraminifera and ostracoda carry additional climate information in their elemental ratios; for example, the ratio of magnesium to calcium varies with ocean-water temperature. Credit: US Geological Survey

Scientists have taken an important step towards overthrowing any remaining concerns about how reliable computer models of the Earth’s climate can be this week. US, UK and Japanese scientists have tested climate models against measurements from fossils that show what sea temperatures were like three million years ago. US Geological Survey scientist Harry Dowsett and his colleagues have often tested models one at a time with such ‘proxy’ measurements. But now they are looking as far back in time as possible, and studying a wide range of models.

“What sets this work apart is that we have carefully evaluated the confidence we have in our proxy data and have begun to look at multiple models,” Harry told Simple Climate. “This is an ongoing process, but these preliminary results using just four models show them to be in good general agreement with each other and the proxy data based estimates.”

Science relies on experiments to test its ideas. If the test’s results don’t fit the theory, then it’s back to the drawing board. Yet our climate is a system enveloping a whole planet. We can’t create a twin planet with slightly higher levels of CO2, for example, to test what will happen if we continue carelessly burning fossil fuels. Today, the next best tool to a twin planet is a computer model. Anyone with everyday experience of computers would be excused for being wary about how much we rely on them. So the sensible thing to do is check they’ve done their job right. But then you run into the problem of planet scale experiments again. Read the rest of this entry »

Fire amid the ice kindles global and local worries

The Anaktuvuk River fire burning in August 2007 on the North Slope of the Brooks Range in Alaska. University of Florida ecologist Michelle Mack and a team of scientists including fellow UF ecologist Ted Schuur found the fire released a significant amount of soil-bound carbon into the atmosphere. Credit: Alaska Fire Service

The Anaktuvuk River fire burning in August 2007 on the North Slope of the Brooks Range in Alaska. University of Florida ecologist Michelle Mack and a team of scientists including fellow UF ecologist Ted Schuur found the fire released a significant amount of soil-bound carbon into the atmosphere. Credit: Alaska Fire Service

In 2007, the largest Arctic tundra wildfire on record released around 2.1 million tonnes of carbon to the atmosphere, adding to the levels of greenhouse gas CO2. That’s close to how much carbon tundra plant growth across the whole Arctic absorbs in one year, noted Michelle Mack at the University of Florida. With human-caused, or anthropogenic, climate change seemingly causing more fires, further CO2 release may contribute to more warming. Other consequences will also have a big local impact, Mack told Simple Climate. “Fire on this landscape will change many things, and that’s frightening for me because I do think that the increasing fires are driven by anthropogenic climate change,” she said. “That people emitting carbon from cities, factories and automobiles very far to the south are influencing this wilderness area where people still practise subsistence livelihood is disturbing to me.”

For about a decade, Mack has been a regular at the Toolik Field Station on the North Slope of the Brooks Range of mountains in far northern Alaska. After the fire started in July 2007 at Anaktuvuk River, a plume of smoke could be seen drifting through the air from the Toolik Field Station 15 miles to the southeast. “When it started it was characteristic of these tundra fires – very small – just a couple of hectares from a lightning strike,” Mack said. “Normally a fire like that would just go out and there would just be a little blackened spot. It wasn’t until August that the weather conditions were such that the fire blew up and burned a really large area. At that time you could see it from space. People in local villages like Anaktuvik Pass and other coastal villages were getting smoked out. People were miserable.”

Read the rest of this entry »

Prehistoric CO2 double-up gives warming data

Electron microscopic picture of microfossils found in drill cores of sediments dating back 40 million years. By studying the remains of such marine plankton - and particularly compounds they produce called alkenones - scientists gain an accurate perspective of past climate change. Earlier, members of the same research team showed that the Arctic Ocean was colonized by similar types of tropical plankton. Scale bar is 20 millimetres, or 0.02 millimetres. Credit: Appy Sluijs

Electron microscopic picture of microfossils found in drill cores of sediments dating back 40 million years. By studying the remains of such marine plankton - and particularly compounds they produce called alkenones - scientists gain an accurate perspective of past climate change. Earlier, members of the same research team showed that the Arctic Ocean was colonized by similar types of tropical plankton. Scale bar is 20 millimetres, or 0.02 millimetres. Credit: Appy Sluijs

The first direct evidence supporting the idea that a recently-discovered period of global warming, one of the hottest in Earth’s history, was caused by CO2 has been published this week. Before the Middle Eocene Climatic Optimum (MECO), which occurred 40 million years ago, temperatures were much higher than today, but steadily falling. However, the MECO was a 400,000 year warming reversal of this trend. Researchers from the Netherlands and UK have now shown that it was accompanied by at least a doubling in atmospheric CO2 levels. Utrecht Univesity’s Peter Bijl and his colleagues also provide cautious estimates for just how much warming can be expected from adding CO2 in top journal Science this week.

Scientists already suspected that the approximately 4°C MECO temperature rise was caused by CO2. “There are only three ways to cause a large and lasting increase in Earth’s average surface temperature,” pointed out Paul Pearson from Cardiff University, UK, who was not involved in the study. “Turn up the heat from the Sun, reflect less sunlight back into space, or trap more heat in the atmosphere.” The heat from the Sun is relatively stable, Pearson comments in a separate article in this week’s Science giving his perspective on the research. Changes in the Earth’s reflectivity due to melting ice tend to happen after climate change has already begun, making greenhouse gases that trap heat around the Earth a likely culprit. Read the rest of this entry »

Of mice, men, and CO2

University of Wisconsin researcher Jessica Blois crawling out or Samwell Cave in California, from where she excavated fossils that she used to determine how small mammals responded to natural climate changes. Credit: Stanford University

University of Wisconsin researcher Jessica Blois crawling out of Samwell Cave in California, from where she excavated fossils that she used to determine how small mammals responded to natural climate changes. Credit: Stanford University

The temperatures predicted as a result of human-driven climate change are likely to be warmer than any that some small mammal species have seen in their evolutionary history. So suggests Jessica Blois, a University of Wisconsin researcher who has studied how the balance between these species has changed over the last 18,000 years. “Presumably, because they have survived to the present, most species can deal with the range of climate change we have seen in the past,” she tells Simple Climate. “But our inferences from the past don’t allow us to predict with as much confidence whether or how they’ll be able to deal with future climates.”

Blois’ work, recently published in the leading journal Nature, used information gathered from fossils in a cave in Northern California to assess the impacts of previous warming periods. She found that one small mammal species – the deer mouse – fared much better than others, like gophers and squirrels, which became increasingly rare. “The data in the paper show that diversity declined with post-glacial warming,” she explains. Read the rest of this entry »