How quickly things change. Only five years ago we were mostly talking about climate change as something that would affect the developed world some decades hence, if not centuries. Sea level rise impacting low-lying countries (i.e. 'not here') towards the end of the century (i.e. 'not in our lifetimes') was probably the prediction that got most attention.

But yesterday the US Government released its latest National Climate Assessment, documenting numerous changes to the American climate that are already happening, in every region of the US and affecting multiple key industries.

They document factors such as increased heavy precipitation events in the north-east, increased drought, water stress and wildfires in the south-west, and increased acidification in the Pacific north-west—already impacting shellfish hatcheries and leading some to shut down and move down the coast.

The authors say they hope their report will provide ammunition for President Obama and Congress to take action. There is certainly room for that. One of the most illuminating maps in the report is a colour-coded map of the US showing status of climate adaptation plans by state: apart from the coastal states, the entire map is blank.

Source: http://nca2014.globalchange.gov/downloads 

Today (or hereabouts) is a special day, but not one you should celebrate. For the first time ever – or at least for the first time in the last 800,000 years that we have good data from ice cores for – the concentration of CO2 in our atmosphere exceeded 400 ppm (monthly averaged readings). 
 
That is Not a Good Thing. More CO2 means more heat trapped in our atmosphere, which will gradually drive up the surface temperature of our planet with unpleasant consequences, such as reduced crop yields, increased diseases and insects in more northerly countries, greater variability in our weather, rising sea levels leading to millions of displaced people... 
 
As a number its nothing special of course, but when you look at it in perspective you appreciate how unusual it really is. Below is the historical CO2 record: the regular zigzags roughly every 100,000 years represent glacial periods, the last one starting around 120,000 years ago and ending about 10-20,000 years ago. Each glacial period was preceded by a sharp rise in CO2 and temperature, which then triggered the glaciation.

The vertical spike on the right hand side is what 400 ppm looks like. W-a-y outside the normal range. Hmm...

Source : http://keelingcurve.ucsd.edu/

A long time ago in a valley far far away there existed a great civilization, known to archaeologists as the Indus Valley Civilization, located in what is today Pakistan and northern India. They did wondrous things, and had highly developed cities in which many houses had individual wells, bathrooms, and an elaborate underground drainage system. The social conditions for their
citizens was superior to those of Egyptians or Babylonians of the time. Life was good.

But around 3800 years ago it all started to fall apart, and until recently no one really understood why. The basics of civilisation crumbled – their standardized system of weights and measures used for trade and taxation fell our of use, as was their unique writing system. Trading links with the Near East were broken. An invasion by Aryan people from India, or a flooding of the Saraswati River, destroying the agricultural system, have both been hypothesized as possible causes.

Now a study of precipitation records from Holocene sediments in an ancient lake in northern India has shown that a major drought event occurred in the area 4100-3900 years ago, linked to a weakening of the annual Indian summer monsoon. Although not conclusive proof, it seems that this had a severe impact on agriculture in the region, which in turn put such a strain on this early urban civilization that it eventually collapsed.

Of course we hope that our own civilization is robust enough to withstand such changes in the weather, that our global transportation systems will allow us to switch food sources, and that there won't be droughts everywhere at the same time. But its yet another sobering reminder of how quickly climate changes can happen and of the inevitability of the consequences (a polite way of saying that if the annual rains fail for a decade, so will the crops, and so will the people who depend on them). 
 
Source: http://geology.geoscienceworld.org/content/42/4/339.full