Three important ways global warming creates problems


UNESCO, Nairobi, Kenya

Rising temperatures have three important effects that create problems.

Erratic precipitation

Where, when and how much rain falls can affect people’s health and livelihoods, and too much or too little precipitation can have devastating effects. Until recently, rain and snow fell in fairly regular patterns that determined, among other things, when farmers plant and harvest crops. But as the oceans and atmosphere have warmed, both the amount of water evaporating and the amount of moisture the air can hold have increased. As a result, we can predict more overall rainfall as the planet continues to warm. But what’s true for one region may be just the opposite for another, leading to more extreme and less predictable precipitation. Most scientific rainfall models predict that high latitude countries, as well as tropical East Africa, will receive more precipitation, while the Amazon Basin, Mediterranean and North Africa, Central America, the Southern Andes, and parts of Australia are likely to receive less. Complex climate phenomena such as the South Asian and West African monsoons are proving harder to model, and for many tropical and subtropical countries, scientists have less confidence in their predictions.

Extreme events

Heat waves, tropical cyclones, extreme rainfall, floods, wildfires and droughts are all examples of natural disasters that may or may not become more common as our climate changes. In 2011, the Intergovernmental Panel on Climate Change (IPCC) produced a special report on such events. It noted that while there is evidence that some extremes have changed since the 1950s, scientists are unsure how much these changes reflect a new reality for different regions and extremes (see Box: Attribution, or “is it climate change?”). That said, climate scientists do predict that climate change will lead to more extreme weather events.

Extreme rainfall raises the risk of soil erosion, landslides and flooding, which can threaten agricultural productivity and infrastructure, posing serious threats to people’s economic and physical security. Floods can also contaminate water supplies and increase the likelihood of water-borne disease, such as cholera. By contrast, too little rainfall can lead to droughts, which can devastate crops and livestock, deplete food supplies and increase the risk of wildfires. According to the 2011 IPCC report on extreme events, in the past 60 years, some regions including West Africa, have experienced more intense and prolonged droughts, whereas regions such as central North America have actually experienced less frequent and less intense droughts than they did in the middle of the 20th century.

Rising seas

Several factors affect sea levels and climate change contributes in two key ways. First, higher atmospheric temperatures lead to higher ocean temperatures, and as water warms its molecules expand, increasing its total volume. Second, rising temperatures also cause glaciers and ice sheets to melt, adding to the total amount of water in the world’s oceans. In July 2013, the World Meteorological Organization reported that that global average sea level rise during the decade 2001-2010 was 3 mm per year, almost double the observed 20th century trend of 1.6 mm per year. Rising seas increase the risk of coastal erosion and floods, which can cause immediate physical damage and injury, threaten health with water-borne diseases, and contaminate drinking water and agricultural land with salt. Small islands and low-lying areas of coastal countries are especially at risk, but this problem is ubiquitous: one in ten people on Earth — some 634 million — live fewer than ten meters above sea level. In Africa, the Niger and Nile Deltas are among the areas most at risk from rising sea levels as they are low-lying, and important centres of both food production and human settlements that are home to millions of people.

Attribution, or “is it climate change?
It is difficult to prove scientifically that any single event is the result of the climate change. Journalists can therefore rarely say for sure whether human activities have made a specific drought or flood or major storm more likely, or whether the event is just part of a natural pattern. However, many extreme events that have occurred already are consistent with what scientists predict climate change will bring, so journalists can always explain individual events in terms of what scientists say about the changing likelihood of such events. As science advances, it may become easier for scientists to demonstrate whether individual events are linked to climate change. In 2012, researchers published a paper that claimed climate change influenced the 2011 drought in East Africa, but that the failure of the 2010 rains was because of natural factors and not climate change.