In evolution’s grand taxonomic journey, fungi—as in sautéed mushrooms—are particularly long-lived survivors. A billion years ago, when the ocean held mainly algae and the land was relatively lifeless (fish did not appear for another 500 million years; modern humans emerged from Africa less than 100,000 years ago), fungi diverged from plants. Today, they form a separate kingdom, distinct from plants, animals and bacteria.

So it seems appropriate that such ancient life forms would serve India with stern, purple warnings of the damage humans have caused to the atmosphere in the geological blink of an eye.

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Agriculture scientists have now identified the immediate cause of the nation’s recent onion shock, where output fell by half and prices rose more than 300%. Two fungi set upon the bulk of the onion crop, causing diseases called purple blotch and purple anthracnose.

Like most fungi, Alternaria porri and —the aptly named—Discula destructiva love dampness. There was plenty of that in India’s onion-growing areas, thanks to the uneven monsoon of 2010 and its unseasonal last gasp in November. Frantic farmers sprayed pesticide on their crop, but it was all washed away as the rain came in unusual fits and starts.

So, was the onion shock a result of climate change, the phenomenon attributed to a rise in global temperatures during the 20th century?

It’s hard to say with any finality. Despite 15 years of climate change consultations (now the largest global negotiations ever), there is no causal evidence that human activity is changing the climate. But there are strong indicators and definite patterns, all of which are getting stronger and more definite.

Since temperature records began in 1880, 2010 tied with 2005 as the warmest year ever. It was the 34th consecutive year that the global temperature was above average. There was an additional complication in 2010—La Nina, a cooling of waters in parts of the Pacific. La Nina occurs naturally, and the link to climate change remains unclear. But scientists explain that whether La Nina, its counterpart, El Nino (which warms the tropical Pacific) or floods, snowstorms or heatwaves, climate change sets off a rise in the intensity and frequency of extreme weather. In sum, this is the cautious reasoning science offers: No individual weather event can be attributed to climate change, but the probability of these events increases as the earth warms. And so winter storms pile up record snows in North America, cyclones spawn epic floods in Australia. Why floods? Warming releases more water vapour, creating more clouds, and more rainfall. Rising temperatures set off cascades of damaging events, such as India’s damaging purple patches. Last week, a study released in the journal Science by a team of British and Brazilian scientists found a 2010 drought, the worst to hit the Amazonian rain forest in a century, risks turning the world’s largest carbon dioxide sink into a carbon emitter so destructive that it could emit more greenhouse gases than the world’s worst emitter, the US, does in a year. The 2010 drought came on the heels of another damaging one in 2005. The two droughts killed many trees, decreasing the Amazon basin’s ability to soak up carbon dioxide, the gas that trees breathe. Worse, the rotting trees are now releasing into the atmosphere this most significant of greenhouse gases, which in a perfect world trap energy (heat) and make life on earth possible.

Without the so-called greenhouse effect, the global temperature would be –18 degrees Celsius Global warming threatens this balance: Thanks to fossil fuels (coal, oil and natural gas), the concentration of carbon dioxide in the atmosphere is now 39% more than it was at the beginning of the 19th century industrial revolution.

Like the great onion shock, the economic effects of global warming are likely to grow.

Last month, German reinsurance company Munich Re counted 1,000 natural disasters in 2010, the highest since 1980. Of these, 90% were weather related. The total damage: $130 billion.

The Russian heat wave that decimated wheat fields in the summer of 2010 has doubled global wheat prices since. In general, unrest over rising prices across the world, whether caused by extreme weather or not, have set entirely unforeseen events into motion. The overthrow of the regime in Tunisia and the ongoing revolution in Egypt began with anger over costly bread, a product of wheat.

The 20th century’s 0.74 degrees Celsius rise may be but a forewarning. This century, temperatures may rise between 1.1 degrees Celsius and 6.4 degrees Celsius, depending on weather patterns and the success humanity has in cooling things down. Don’t be too hopeful. Despite 16 meetings over 15 years, negotiators can’t agree on holding warming to a rise of even 2 degrees Celsius, which in itself may be inadequate—a rise of 1.5 degrees Celsius may inundate island nations. Later this year, negotiations move to Durban, South Africa. Barring a miracle, India should get ready for more purple patches.

Samar Halarnkar is editor-at-large, Hindustan Times. This is a fortnightly column that explores the cutting edge of science and technology. Comments are welcome at