Comment: How long have humans been altering Earth's climate?

Thu, 07 Apr 2016 18:48:29 -0400

The early anthropogenic hypothesis holds that prolonged warmth in the Holocene was caused by early agriculture. Paleoclimatologists have long sought an analog of the current Holocene interglaciation. Here, precession (A) and obliquity (B), which impact solar insolation, and atmospheric carbon dioxide concentrations (C) of previous interglaciations are compared with the Holocene (stage 1). The closest analog to the Holocene is stage 19, which began about 787,000 years ago. Credit: Ruddiman et al., Review of Geophysics, 2016.

Throughout the 20th century the paleoclimate science community regarded the warmth of the current (Holocene) interglaciation — prior to the major anthropogenic intervention of the last 150 years — as overwhelmingly natural in origin. In this view, changes in Earth’s orbit had resulted in increased summer insolation at high latitudes of the Northern Hemisphere, which began melting the North American and Scandinavian ice sheets 17,000 years ago and eventually ushered in interglacial warmth. Although further orbital shifts then led summer insolation to begin decreasing 10,000 years ago, the drop was thought not to have been substantial enough to cause renewed glaciation.

Giant dunes, not mega-tsunami deposits?

Thu, 05 Jan 2012 06:41:58 -0500

Some models suggest the chevrons' orientations (black arrows) don't match the direction of arriving tsunami waves (white arrows). Robert Weiss

Tsunamis generated by asteroid impacts may have left white, sandy "chevron" deposits in Madagascar. Robert Weiss

About four years ago, a group of scientists proposed that a series of giant, wedge-shaped sandy deposits found along the shores of southern Madagascar might be evidence of a giant tsunami — a “mega-tsunami” — generated by an asteroid that may have blasted into the Indian Ocean sometime in the last 10,000 years. Furthermore, the scientists said, such impacts and the resulting tsunamis may have occurred fairly frequently during this period. To search for evidence of these impacts, the researchers formed the Holocene Impact Working Group. By 2006, with the help of Google Earth, they found dozens more of the wedge-shaped deposits, called chevrons, scattered across the planet, including in Africa, Australia and the United States.

Holocene on EARTH Magazine

Comment: How long have humans been altering Earth's climate?

Giant dunes, not mega-tsunami deposits?