A new University of Colorado Boulder-led study appears to answer contentious questions about the onset and cause of Earth's Little Ice Age, a period of cooling temperatures that began after the Middle Ages and lasted into the late 19th century.
According to the new study, the Little Ice Age began abruptly between A.D. 1275 and 1300, triggered by repeated, explosive volcanism and sustained by a self- perpetuating sea ice-ocean feedback system in the North Atlantic Ocean, according to CU-Boulder Professor Gifford Miller, who led the study. The primary evidence comes from radiocarbon dates from dead vegetation emerging from rapidly melting icecaps on Baffin Island in the Canadian Arctic, combined with ice and sediment core data from the poles and Iceland and from sea ice climate model simulations, said Miller.
Low sun spot activity to blame? Nope. The big cooling was all about cooling aerosols ejected by volcanoes.
Most scientists think the Little Ice Age was caused either by decreased summer solar radiation, erupting volcanoes that cooled the planet by ejecting shiny aerosol particles that reflected sunlight back into space, or a combination of both, said Miller.
The new study suggests that the onset of the Little Ice Age was caused by an unusual, 50-year-long episode of four massive tropical volcanic eruptions. Climate models used in the new study showed that the persistence of cold summers following the eruptions is best explained by a sea ice-ocean feedback system originating in the North Atlantic Ocean.
"This is the first time anyone has clearly identified the specific onset of the cold times marking the start of the Little Ice Age," said Miller. "We also have provided an understandable climate feedback system that explains how this cold period could be sustained for a long period of time. If the climate system is hit again and again by cold conditions over a relatively short period -- in this case, from volcanic eruptions -- there appears to be a cumulative cooling effect."
When will nature throw another really big curve ball at us?
Megadrought. What a great word. Not tinny at all. Looking at the previous interglacial most like our current Holocene era some climate history researchers found that the US southwest can undergo a megadrought during a warmer interglacial such as the interglacial we are currently in.
In a letter published recently in the journal Nature, Los Alamos National Laboratory researchers and an international team of scientists report that the Southwest region of the United States undergoes "megadroughts"ówarmer, more arid periods lasting hundreds of years or longer. More significantly, a portion of the research indicates that an ancient period of warming may be analogous to natural present-day climate conditions. If so, a cooler, wetter period may be in store for the region, unless it is thwarted by increased concentrations of greenhouse gasses in the atmosphere that could warm the planet.
In a previous interglacial known as Marine Isotopic Stage 11 the southwest experienced a drought lasting thousands of years.
The oldest warm period in MIS 11 appears somewhat analogous to the present-day Holocene interglacial period, which has been ongoing for about the past 10,000 years. During MIS 11, the ancient climate warmed dramatically by about 14 degrees Fahrenheit. This warming in the wake of a preceding period of cold gave rise to an abundance of plant life and seasonally wet conditions. As warming continued, grasses and shrubs died off and lakes dried up. The ensuing drought lasted thousands of years before ending abruptly with a cooler, wetter period.
The world's human population has exploded during this interglacial. Humans have spread into regions which are more hospitable than they were in at least part of previous interglacials. If only we had a better understanding of climate we might be able to predict our risk for megadroughts in regions around the world. Such prediction would give us more time to prepare.