The manmade changes pushing the planet toward a critical transition
Nature changes gradually—until it doesn’t. As the changes in an ecosystem pile up, they can push the system past a “critical threshold,” and then the change can become extremely fast (in relation to geological timescales) and unstoppable. And in a review in the journal Nature, researchers suggest that the same thing is happening to the whole world: Humans could be driving Earth’s biosphere towards a tipping point beyond which the planet’s ecosystems will collapse abruptly and irreversibly.
This global ecosystem collapse has occurred before, most recently about 12,000 years ago with the last transition from a glacial period to the current interglacial (i.e., warm) period, say the review authors. Over the relatively short period of 1,000 years, fluctuations in the Earth’s climate largely killed off about half the large mammal species, along with birds, reptiles, and a few smaller mammal species. The millennium-long shift was triggered by rapid global warming, and once this warming pushed the planet past its tipping point, the end of the 100,000-year-old ice age became inevitable, giving way to the current 11,000-year-old interglacial era.
If you could watch a movie of the planet over the last several million years, you’d see the ice caps advance and retreat: The planet’s climate moves in cycles, with ice ages and interglacial periods alternating. But looking at previous interglacials similar to our own, geophysicists now think that the current mostly ice-less period may be longer than it would have been had a certain species not invented the combustion engine. Specifically, it looks like with amount of greenhouse gases we’ve already spewed into the atmosphere, the next ice age will be delayed. And before you decide that’s a good thing, at the rate we’re currently going, we’re not just pushing off the glaciers for a few geologically insignificant years: the team says that the atmospheric concentration of CO2 would to be at most 240 parts per million (ppm) before glaciation would kick in. Right now, it’s 390 ppm, with no signs of dropping and many signs of continuing to rise. When (and how) the planet’s self-regulation system will kick in isn’t clear, but the long, increasingly hot trip probably isn’t going to be pretty.
Read more at the BBC.
Image courtesy of NASA / Wikipedia
Scientists have often wondered how woolly mammoths survived and thrived in the frigid climes of the far north in Earth’s last ice age. The hemoglobin in elephant (and human) blood cannot easily transfer oxygen to other cells in the body at low temperatures. Instead, the blood’s hemoglobin holds onto its oxygen in icy extremities and the tissue eventually dies; that’s the main reason we get frostbite. There must, then, have been something special about mammoth hemoglobin.
Putting on clothing to protect our woefully hair-deficient bodies is one of the key moments in the history of becoming human. Just when our species took this step, however, is open to a fair amount of guesswork—scientists can’t exactly dig up fossilized parkas and trousers. But what scientists can do is determine roughly when two species diverged, and that has made all the difference: Using the lice that have traveled with people for thousands of years, a team has tracked the time that humans first became dedicated followers of fashion—perhaps as long as 170,000 years ago.
The key to the study by David Reed and colleagues, which appears in Molecular Biology And Evolution, is that there are two kinds of lice that hang around humans: the head lice that live on our scalp, and the body lice that live in our clothes. At one point in the past these two shared a common ancestor, Reed reasoned, and the body lice would have split off and become a separate group once they had human clothing in which to live.
So if we can figure out when they arrived at the scene, we’d have a minimum age on clothes. Thanks to modern molecular techniques, we can compare the genomes of these two lice and come up with that date. For the curious, a “Bayesian coalescent modeling approach” tells us that we were going clothed at least 83,000 years ago, and maybe as far back as 170,000 years. [Ars Technica]
Before we humans came along with our Industrial Revolution and our greenhouse gases, the earth was hurtling towards an intense ice age that could have covered much of the northern hemisphere with deep ice sheets as soon as 10,000 years from now, according to a tentative new study. But that’s no reason to thank our lucky stars for global warming, says study coauthor Thomas Crowley: “We’re creating a situation at least as dangerous, only going in the opposite direction” [Wired News].
Climate data shows that complex life evolved on a much warmer “hothouse earth,” and that the planet has been gradually cooling for the last 50 million years. Then, 2.5 million years ago, the climate entered a curious new phase: it started oscillating wildly, see-sawing between interglacial periods with conditions similar to today’s and ice ages during which the amount of permanent ice in the northern hemisphere expanded hugely. At the peaks of these transient ice ages, much of northern Europe, northern Asia and North America were covered in ice sheets [more than 2 miles] thick, and sea levels were [almost 400 feet] lower than today [New Scientist]. The new study argues that this period of oscillations was a transition to a stable, long-term ice age that would have made those previous ice ages look like mere cold snaps.
After running a batch of 300-year-old Stradivarius violins through a sophisticated medical scanner, researchers say they may have figured out why the aged instruments are revered for their tone, clarity, and power: The wood used for the ancient violins shows a more consistent density than that found in modern violins, and researchers argue that this difference may affect how vibrations travel through the wood.
In particular, the old wood shows less variation in density within growth rings, researchers say. Tree rings are comprised of a lighter, spongier portion that is produced during rapid spring growth and a darker, denser portion produced later in the year; in the Stradivarius wood these differences are less pronounced. Other researchers who have studied the activity of the Sun have pointed to a mini-Ice Age that occurred in the early 1700s. Experts say that this reduced solar activity, called the Maunder Minimum, could have hampered the regular growth of trees [BBC News].
The Earth was an inhospitable place 635 million years ago, with ice sheets that extended to the equator. Scientists have long wondered how the planet rebounded from that icy era, known as “Snowball Earth.”
Now a new study suggests that a stream of methane gas escaping from the ice brought the planet to a climate tipping point and transformed it into a lush, tropical world, in what researchers called one of the most severe climate change events recorded in Earth history [Nature, subscription required].
Paleoclimatology has become a hot field, as researchers believe that the planet’s dramatic prehistoric climate shifts can help predict the effects of present-day global warming. Since methane figures into one of the most ominous global warming scenarios, this latest study is being eagerly scrutinized for clues to our planet’s fate.