Don Bogard, isotopic and nuclear geochemistry: Today, when many are concerned about the Earth possibly over-heating through greenhouse warming, it is worthwhile to look into the not very distant past when the Earth over-cooled. Most people have heard of the Ice Age but probably know very little about it. Some may remember climate scientists in the 1970s expressing concern that Earth may be entering a new ice age, because of growing evidence that Earth was cooling (in spite of growing atmospheric carbon dioxide of CO2). What was the ice age, why did it occur, and is it now in our past, or also in our future?
Sebastian Luening, paleogeologist, Hui Su, Jet Propulsion Lab, USA et al., Andrew Follet: Most global climate models are underestimating increased rainfall caused by global warming. NASA and four universities compared climate data from 1995 to 2005 to 23 climate model simulations for the same period. More than 70 percent of the climate models underestimated the amount of rain compared to the real world observations. “Precipitation is vital to life on Earth and regional precipitation changes accompanying anticipated global warming could exert profound impacts on ecosystems and human society,” reads the study’s abstract.
Cameron Petrie, archaeologist: With climate change in our own era becoming increasingly evident, it’s natural to wonder how our ancestors may have dealt with similar environmental circumstances. New research methods and technologies are able to shed light on climate patterns that took place thousands of years ago, giving us a new perspective on how cultures of the time coped with variable and changing environments. An article in Current Anthropology explores the dynamics of adaptation and resilience in the face of a diverse and varied environmental context, using the case study of South Asia’s Indus Civilization (c.3000-1300 BC).
Sarah Kaplan, The Washington Post: About 700 million years ago, Earth turned into a snowball. The polar ice sheets expanded until they engulfed the globe. The oceans turned to slush. The vast expanses of ice and snow reflected the sun's light back into space, exacerbating the endless winter. Temporary relief came in the form of massive volcanic eruptions, which spewed carbon dioxide into the atmosphere and triggered a period of global warming. But that, too, spiraled out of control. Earth became a greenhouse — its oceans hot enough to cook their inhabitants, its blighted landscape further ravaged by floods. Then, suddenly, something about the shifting continents or ash-darkened skies prompted the planet to cool again. The snowball returned.
Andrew Kenny, physicist and mechanical engineer: This article discusses CO2 levels and global temperatures over the last 550 million years, roughly the period of multi-celled life. CO2 has averaged about 2,000 ppm over this time but with huge fluctuations. Temperatures by contrast have been remarkably steady except for three periods of cold (when there was ice at the poles) and a period of semi cold.
Sebastian Luening, Geologist, Paleontologist, publisher of kaltesonne.de: The website: kaltesonne.de brings very interesting articles in German and English together for a consistent discussion on the history of Earth's climate. This article shows that several thousand years ago Greenland had less ice than today. Principal components analysis reveals two dominant Holocene trends, one with early Holocene warmth followed by cooling in the middle Holocene, the other with a broader period of warmth in the middle Holocene followed by cooling in the late Holocene. The temperature decrease from the warmest to the coolest portions of the Holocene is 3.0 ± 1.0 °C. The Greenland Ice Sheet retracted to its minimum extent between 5 and 3 thousands of years ago, consistent with many sites from around Greenland depicting a switch from warm to cool conditions around that time.
Doug Hurst is a retired RAAF navigator with a long-term interest in weather and climate. In writing this article he was assisted by: Ex-RAN engineers Colin Davidson and Peter Bobroff; epidemiologist Dr Judy Ryan; IT specialist Mike O’Ceirin; medical practitioner Dr Patrick Purcell; public servant and military historian Peter Edgar; polymath Peter Kemmis; biochemist Maureen Hanisch; novelist and poet Alan Gould; and geologists Aert Driessen and Dr Howard Brady, author of Mirrors and Mazes, a guide through the climate change debate.
Simon Armitage, Royal Holloway University, Charlie Brislow, University of London, Nick Drake, Kings College, London, UK.: North Africa was wetter 15,000–5,000 years ago than today. We reconstruct the lake-level history of Lake Mega-Chad, when it was the largest African lake, and demonstrate that this humid period ended abruptly 5,000 years ago, indicating that the African monsoon exhibits a nonlinear response to insolation forcing. The northern basin of Lake Mega-Chad, currently the world’s greatest dust source, became dry around 1,000 years ago.