Scientists worry about the growing threat of climate change because the global climate is tied to everything that society cares about: human and environmental health, food and industrial production, water availability, extreme events, and more. Figuring out how all these pieces tie together is difficult. And many of us, from scientists to the public to policy makers, have only a partial understanding of the true implications of a changing climate for our economies, societies, and the world around us. But we already know enough to be worried. Here is just one example: the connections between climate, snow, ice, and water resources.
My early research on climate and water showed that climate changes were likely to reduce the amount of snow we get in mountainous areas, increasing the chances of rain instead of snow and accelerating snowmelt. Since then, more and better research has confirmed and expanded this understanding. In the late 1980s, this was all hypothetical – it is what our models told us was likely to happen with warming. Those models proved correct, and we now see these and many other changes occurring. Some of these scientific findings were recently summarized in the latest, compelling IPCC release, but as an example, scientists now state that:
There is very high confidence that the extent of Northern Hemisphere snow cover has decreased since the mid-20th century.
It is likely that there has been an anthropogenic contribution to observed reductions in Northern Hemisphere spring snow cover since 1970.
Human influence has been detected in warming of the atmosphere and the ocean, in changes in the global water cycle, in reductions in snow and ice, in global mean sea level rise, and in changes in some climate extremes. This evidence for human influence has grown since [the previous IPCC report]. It is extremely likely that human influence has been the dominant cause of the observed warming since the mid-20th century.
And projections for the future continue to be worrisome:
By the end of the 21st century, the global glacier volume, excluding glaciers on the periphery of Antarctica, is projected to decrease by 15 to 55% for [the low emissions scenario], and by 35 to 85% for [the high emissions scenario] (medium confidence).
The area of Northern Hemisphere spring snow cover is projected to decrease by 7% for [the low emissions scenarios] and by 25% in [the high emissions scenarios] by the end of the 21st century for the model average (medium confidence).
Our water systems are complex. But many climate impacts are actually pretty simple to understand. Let’s focus for the moment on just one piece of the climate change picture: rising temperatures. We know the Earth is warming up because of human activities – as recently described, scientists are as confident of this as we are that smoking tobacco causes cancer. Warming alone means that more precipitation will be rain and less will be snow. Higher temperature also means that what does fall as snow will melt faster, run off earlier into our rivers and streams, and evaporate more quickly back to the atmosphere.
Take the Himalayas as an example. The Hindu Kush-Himalayan region (HKH) covers parts of eight countries (Afghanistan, Bangladesh, Bhutan, China, India, Nepal, Myanmar and Pakistan), contains many of the biggest mountains in the world, and has the largest glaciers. These mountains are the headwaters of some of the world’s great rivers as well – including the Ganges, Indus, Brahmaputra, Salween, Mekong, Yellow, and Yangtze. These rivers provide drinking and irrigation water for at least one and a half billion people. Even with the accelerating climate changes, the HKH region are expected to have glaciers for centuries, but as temperatures rise, lower elevation glaciers and snow will melt, recede, and disappear, affecting water availability and especially, the timing of flow. (A few of the many scientific assessments about this are here, here, here, and here.)
The eastern Himalayas and the Tibetan Plateau are already warming, like the rest of the planet. Glacial retreat, especially in the central and eastern Himalayas, is already occurring. Lower elevation glaciers are disappearing faster than higher (and colder) ones. Some rivers are already experiencing seasonal or annual increases in flow as ice melt grows. These are the regions likely to be on the front line of any challenges to water resources from climate change.
Water supplies in North America from the Rocky Mountains, the Cascades, and the Sierra Nevada are also at risk: Expect to see rising snowlines. Expect growing winter flows and flood risks as snow turns to rain and decreasing summer flows as the snow disappears earlier and earlier in the year. Expect to see local glaciers shrink and disappear, as is already happening in Glacier National Park.
[In a straight-faced comment on the website of the famous Glacier National Park in the United States, the National Park Service states: “Despite the recession of current glaciers, the park’s name will not change when the glaciers are gone.” Maybe that’s fitting: the disappearance of glaciers in Glacier National Park will be a mark of our failure to act.]
Significant climate changes will occur because we’ve taken too long to acknowledge and react to the problem. And that means unavoidable impacts for water resources (and other things), and inevitable adaptation and reaction. The (somewhat) good news is that planning and acting now can help reduce the worst consequences later. There are plenty of things we can do, including improved water-use efficiency and cutting waste, better planning for floods and droughts, advanced monitoring and warning systems for extreme flood events (such as we’ve just seen with the successful evacuations for Typhoon Phailin), more sophisticated reservoir operations, and stronger institutions to manage water and reduce water conflicts. I will continue to address some of these issues in future posts.
[This is an update from an earlier post, with information from the latest IPCC science summary.]