Until modern times, climate had been a major restriction to population growth but the advent of fossil fuels has allowed widespread pumping of ground water to grow more crops. This fossil water is however a limited resource and becoming rapidly depleted in many parts of the world.
When ground water is exhausted, the affected region becomes dependent on food imports and this pattern has been repeating with increasing frequency and scale. Libya, Yemen, Saudi Arabia, Syria, Iran and Iraq to name a few. Until recently, India and China were self sufficient in basic foods but with falling water tables in the Punjab and north China plain, both have rapidly become major wheat importers.
While wealthy countries have been able to import food to balance shortfalls, less prosperous nations have not. Often the result has been internal unrest and instability. This process has been exacerbated by global warming which has increased the severity of droughts and driven greater fluctuation in food stocks available on international markets.
Climate change is projected to cause average declines in key food commodities such as wheat and rice even as world population continues to rise. Of more concern is the effect on volatility in in food supplies which in turn leads to political instability and market disruptions.
To date, national conflicts over water have been rare but the depletion of groundwater stocks is leading to a scramble to claim other sources. China is damming and diverting headwater sources to the Brahmaputra and Mekong rivers on which many other nations depend. India controls much of the headwaters for key rivers in Pakistan and both countries simply cannot have more of the same resource. Egypt has threatened to destroy a dam being constructed in on the Blue Nile in Ethiopia though a temporary deal has been struck.
It seems unlikely that nations would go to war solely over water but as shortages become more severe this source of tension may add to others and war might become a political expedient to distract populations from domestic unrest.
Global warming and groundwater depletion are putting the squeeze on food security. The political consequences will reach all nations and add to the direct impacts of irreversible climate destabilisation.