by T. R. Ramachandran and T. R. Shankar Raman
(This article appeared as a lead on the edit page of The Hindu on 13 July 2013)
The recent flood-related disaster in Uttarakhand was labelled a Himalayan tsunami, recalling the deaths, damage, and destruction that followed the Indian Ocean earthquake and tsunami of December 2004. Yet, this is a misleading metaphor, because there is little evidence that real tsunamis are linked to human activities that impact our oceans or sea-floors. In contrast, there is compelling evidence that climate change and the occurrence of extreme meteorological events—such as the one in Uttarakhand—are also related to human activities that have altered our atmosphere through greenhouse gas emissions. In today’s world, many weather-related disasters are not merely chance occurrences.
Extreme weather and related disasters are becoming more common. In an analysis published in 2012, Munich Re, the global insurance giant, reported that disasters tied to extreme weather events have more than doubled worldwide since 1980. So far in 2013, many examples stand out—record high temperatures in Australia and the US (including the highest June temperature—54.0°C—in Earth’s recorded history at Death Valley, California), heavy rainfall and catastrophic floods in northern India, USA, Canada, Central Europe, and Argentina. Parts of the central US also experienced record snowfall as late as May. Simultaneously, other parts of the US, such as southern Texas, are in the midst of record drought.
Extreme temperature swings are also increasingly common. Having endured a “bone-chilling” cold wave in January, parts of India were in the grip of a massive heat wave in May, and the risk of such heat waves is predicted to increase. Such swings are not uncommon in the US either. For instance, according to the US National Oceanic and Atmospheric Administration (NOAA), the city of Lincoln in the state of Nebraska registered a record low of -0.5°C on 12 May, rising to a record high of 37.7°C within two days!
What’s behind these extremes? Is global warming responsible? After all, NOAA reported that the global average temperature for May 2013 tied with 1998 and 2005 as the third warmest May in 134 years of record-keeping. However, any single extreme weather event or natural disaster cannot be attributed solely to global warming, because day-to-day temperatures and long-term climate are also influenced by natural variability in local weather, larger-scale atmospheric and oceanic oscillations, and other factors such as solar cycles, volcanoes, and atmospheric pollution. Moreover, how could global warming be linked to both extreme heat and cold, or cause both record droughts and rainfall, snowfall, or floods?
Global warming refers to an increase in the worldwide average temperature, as has been observed in the last few decades. With an average trending higher, both record heat and cold events can and do occur, but more heat records are observed than cold as the overall distribution of temperatures shifts higher. In USA, for example, the ratio of record high-to-low temperatures has been increasing markedly since the 1970s, and is projected to increase even more dramatically in the future. Justin Grieser of the Washington Post reported that in Washington, D.C.,
daily heat records have outnumbered cold records… by a 7 to 1 ratio since… 2000 and by nearly 16 to 1 in the past 3.5 years.
According to a just-released report from the World Meteorological Organization titled The Global Climate 2001–2010: A Decade of Climate Extremes, a qualitatively similar trend is also evident worldwide in the last two decades.
Another way to view this shift is through the results of scientist James Hansen‘s team at NASA, which showed that, as average temperatures rise, the overall temperature distribution shifts higher, and heat extremes that would have had a very low probability of being observed 30 years ago are observed much more frequently today. The evidence is strong that global warming is the culprit: in a new paper in the journal Climate Change, climate scientist Dim Coumou and colleagues note that:
… worldwide, the number of local record-breaking monthly temperature extremes is now on average five times larger than expected in a climate with no long-term warming.
Unusual cold temperature records are also accruing, especially in the northern hemisphere. Strangely enough, a key reason for this is believed to be the extreme warming of the Arctic at twice the rate of the rest of the northern hemisphere (Arctic Amplification). As scientists Jennifer Francis and Stephen Vavrus have shown, drastic Arctic summer sea ice melt since the 1980s (equivalent to ~40% of the contiguous US land area, almost equal to land area of India) and concomitant heat transfer to the Arctic Ocean could cause significant anomalies in atmospheric weather patterns, particularly in the north polar jet stream air current. As the anomalous jet stream meanders and lingers over parts of North America and Eurasia, it results in prolonged, extreme heat or cold events. Thus, increased temperature extremes are not just chance occurrences but partly due to global warming.
What about droughts and floods? The 2007 IPCC report observed that with global warming most climate models predict increased summer dryness and winter wetness in the northern hemisphere. Extended periods of high surface temperatures without adequate moisture and with a higher atmospheric capacity to hold water vapour can lead to drier soils and drought. There is growing evidence that global warming is partly the cause of the significant increase in aridity across the globe since the 1970s and associated record forest fires. At the same time, the vast majority of the warming in the last few decades has occurred in the world’s oceans. Greater evaporation of water into a warmer atmosphere capable of holding more water vapour has led to an increase in atmospheric water content by about 4% since the 1970s. With such moisture-laden air delivered over land by storms, the likelihood of more extreme rainfall or snowfall and ensuing floods in some regions is increasing, as observed in the US and India. As scientist Kevin Trenberth remarked:
… all weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.
What can we do about these disturbing trends? First, let’s recognize the key cause of warming. There is now clear, overwhelming, among 97% of climate scientists that current warming is largely man-made, fuelled by emissions of greenhouse gases such as carbon dioxide (CO2) from fossil fuels and human activities. In May 2013, the CO2 concentration in our atmosphere crossed 400 parts per million (ppm), up from about 280 ppm in the late 1700s. The last time the CO2 level was as high as 400 ppm was around 3 – 5 million years ago, when sea levels were much higher and regional climates were very different. Where we are today is unprecedented since the advent of modern human civilization.
Second, we need to dramatically reduce greenhouse gas emissions and do so collectively across the world. Extreme weather events are not partial to developed or emerging economies. A global climate risk index indicates that warming is affecting most of the globe, especially Asia. The economic impact of climate change is also significant and growing. We must therefore accelerate a shift worldwide—away from fossil fuels and heavily carbon-intensive activities, towards new economic growth engines based on renewable energy, energy efficiency, and carbon sequestration.
Finally, human management of land and forests, rivers, and industrial livestock also impact emissions and can significantly influence the aftermath of extreme weather events. The Uttarakhand floods illustrated what could happen when an extreme weather event intersects poor mitigation and adaptation practices, ranging from unrestricted logging and construction on landslide-prone slopes to poor disaster management. Environmental mismanagement, too, can accentuate disasters. When natural forests and grasslands of mixed native species are destroyed, degraded, or converted to monoculture plantations of alien species it alters soils, reducing soil moisture retention and infiltration. This can make soils more prone to erosion and contribute to the twin travails of destructive floods and drying watersheds. A study from near Nainital in the Kumaun Himalayas by P. K. Rawat showed that, between 1985 – 1990 and 2005 – 2010, the decline in natural oak forest cover and increase in barren land and mixed forest was accompanied by a 62% increase in soil erosion rate, 15% increase in flood runoff, and greater density of landslides in the watershed.
Still, this scenario can be turned around: conserving natural forests and grasslands helps avoid increased emissions, minimise soil erosion and surface runoff, increase water retention and sustain flows longer into the dry season, and buffer the impact of high rainfall events. Uttarakhand and other recent disasters are warnings to us highlighting the need to look beyond just near-term expediency and incorporate greater sensitivity to environment and climate concerns in our best practices across all sectors. Meanwhile, the climate clock is ticking.
T. R. Ramachandran is a Vice President at LSI Corporation in California, USA, and T. R. Shankar Raman is a Senior Scientist with Nature Conservation Foundation, Mysore. The views expressed here are solely those of the authors and do not necessarily reflect the views of their organisations.