Mayan collapse due to drought

The Maya civilization was among the most advanced in history, and its disintegration has perplexed researchers for ages. One of the most compelling theories to date suggests that a shifting climate, playing puppeteer to sociopolitical marionettes, had a devastating role in the Maya's downfall. Now, researchers have combined remarkably detailed climate data — recorded in a Central American stalagmite — with historical records to help determine what really happened to this mysterious Mesoamerican society.

http://io9.com/5958954/what-destroyed-the-maya-a-stalagmite-from-beliz-could-finally-solve-this-ancient-mystery

Why is Antarctic sea ice growing if the world is getting warmer?

Sea Ice in the North

Sea Ice in the South

As the Arctic was experiencing a record low minimum extent, the Antarctic was reaching record high levels in the satellite record, culminating in a winter maximum extent of 19.44 million square kilometers (7.51 million square miles) on September 26. The September 2012 monthly average was also a record high, at 19.39 million square kilometers (7.49 million square miles) slightly higher than the previous record in 2006.

The September extent trend for 1979 to 2012 is just above the statistical significance level (0.9% per decade, plus or minus 0.6%). The new Antarctic sea ice September value is slightly greater than typical year-to-year variations, and is roughly equal to a 25 mile (40 kilometer) northward shift in the location of the ice edge relative to the 1979 to 2000 average. The trend for ice extent growth during Antarctic winters is about 16,000 square kilometers per year (6,200 square miles) or roughly an area the size of Connecticut. In comparison, the decline in Arctic summer sea ice extent is an area about the size of Indiana (91,600 square kilometers per year, or about 35,400 square miles).

Our colleague, Dr. Sharon Stammerjohn of INSTAAR, University of Colorado, provides a review of the differences between Arctic and Antarctic climate controls on sea ice and helps place the events in context. First, climate is warming over much of the Antarctic continent, as shown in several recent studies (e.g., Chapman and Walsh, 2007, Monaghan et al., 2008, Steig et al., 2009) and is related to Pacific Ocean warming (Ding et al., 2010) and circumpolar winds. Both warming and ozone loss act to strengthen the circumpolar winds in the south. This is due primarily to persistently cold conditions prevailing on Antarctica year-round, and a cold stratosphere above Antarctica due to the ozone hole. Stronger winds generally act to blow the sea ice outward, slightly increasing the extent, except in the Antarctic Peninsula region, where due to geography, winds from the north have also increased, pushing the ice southward. Thus, sea ice extent near the northwestern Antarctic Peninsula continues to decline rapidly, while areas in the Ross Sea and the southern Indian Ocean show significant increases (Stammerjohn et al., 2012). Circumpolar-averaged sea ice extent changes nearly cancel each other out for all months of the year (Parkinson and Cavalieri, 2012). This winter, atmospheric conditions were near average overall, with roughly equal areas of cooler and warmer air temperatures over the sea ice.

Comparing winter and summer sea ice trends for the two poles is problematic since different processes are in effect. During summer, surface melt and ice-albedo feedbacks are in effect; winter processes include snowfall on the sea ice, and wind. Small changes in winter extent may be a more mixed signal than the loss of summer sea ice extent. An expansion of winter Antarctic ice could be due to cooling, winds, or snowfall, whereas Arctic summer sea ice decline is more closely linked to decadal climate warming.

http://nsidc.org/arcticseaicenews/2012/10/poles-apart-a-record-breaking-summer-and-winter/

Food prices cause social unrest

Food prices (black line) and food riots and the Arab Spring (red lines)

The timing of violent protests in North Africa and the Middle East in 2011 as well as earlier riots in 2008 coincides with large peaks in global food prices.

If food prices remain high, there is likely to be persistent and increasing global social disruption.

http://necsi.edu/research/social/foodcrises.html

The food price threshold at which increased social unrest occurs may be passed again soon:

Food prices (blue) and food price model (red) including projected increases in coming months. The social unrest threshold, corrected for inflation (purple dashed line) is a level of food prices that is likely to cause food riots of impoverished populations and social disruption. 

http://necsi.edu/research/social/foodprices/briefing/

Global water use from 1900 to 2000 by sector

The greyband represents in the difference between the amount of water extracted and that actually consumed. Water may be extracted, used, recycled (or returned to rivers or aquifers) and reused several times over. Consumption is final use of water, after which it can no longer be reused. That extractions have increase at a much faster rate is an indication of how much more intensively we can now exploit water. Only a fraction of water extracted is lost through evaporation.

http://www.grida.no/graphicslib/detail/trends-in-global-water-use-by-sector_f83a

Hans Rosling

Arctic sea ice

Arctic sea ice has hit a record low.

This year’s minimum was 760,000 square kilometers (293,000 square miles) below the previous record minimum extent in the satellite record, which occurred on September 18, 2007. This is an area about the size of the state of Texas. The September 2012 minimum was in turn 3.29 million square kilometers (1.27 million square miles) below the 1979 to 2000 average minimum, representing an area nearly twice the size of the state of Alaska. This year’s minimum is 18% below 2007 and 49% below the 1979 to 2000 average.

http://nsidc.org/arcticseaicenews/2012/09/arctic-sea-ice-extent-settles-at-record-seasonal-minimum/

Arctic sea ice is melting much faster than predicted.

IPCC models vs observed sea ice.

Tropical Forests make poor farmland

With all the lushness and productivity that exist in tropical forests, it can be surprising to learn that tropical soils are actually very thin and poor in nutrients. The underlying “parent” rock weathers rapidly in the tropics’ high temperatures and heavy rains, and over time, most of the minerals have washed from the soil. Nearly all the nutrient content of a tropical forest is in the living plants and the decomposing litter on the forest floor.

The organic material and nutrients in a tropical rainforest are found in the vegetation itself, not in the soil. This eroded hillside along a river in Amazonia shows the infertile soil typical of tropical environments (pinkish-tan) topped by a very thin layer of fertile soil and forest detritus (brown). 

When an area is completely deforested for farming, the farmer typically burns the trees and vegetation to create a fertilizing layer of ash. After this slash-and-burn deforestation, the nutrient reservoir is lost, flooding and erosion rates are high, and soils often become unable to support crops in just a few years. If the area is then turned into cattle pasture, the ground may become compacted as well, slowing down or preventing forest recovery.

All tropical forest sub-regions (coded by color) are represented in a list of the top 20 countries that cleared the most forest between 1990 and 2005. Brazil, the leader, cleared over 42 million hectares, an area the size of California. 

http://earthobservatory.nasa.gov/Features/Deforestation/printall.php

World GDP per capita 1500 to 2003

World GDP per capita 1500 to 2003

http://en.wikipedia.org/wiki/World_economy

Population growth

World human population (est.) 10,000 BC–2000 AD.

World population since 1950

A chart of changes in world population growth rate from 1950–2010 (red) and predicted changes in world population growth rate from 2010–2050 (blue).

http://en.wikipedia.org/wiki/Population_growth