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Many claims are made that climate change is increasing disasters, particularly water and weather-related disasters such as floods, hurricanes and heat waves.
But such claims make a basic scientific error: Weather hazards and disasters are not the same thing. A disaster requires both a weather hazard and lack of preparedness for it.
A dangerous environmental event such as a tornado or a landslide is a "hazard." It is influenced by climate and climate change.
The other, and usually more important, half of the equation is the human and societal inability to cope with that event, termed "vulnerability".
Vulnerability arises when houses are built in a floodplain, when people cannot afford insurance or when governments allocate money to weapons instead of addressing disaster risks. Climate and climate change do not necessarily influence vulnerability.
HAZARD PLUS VULNERABILITY EQUALS DISASTER
For a disaster to occur, both a hazard and vulnerabilities to it need to be present. Climate change mainly affects hazards, changing the rates, sizes, and locations of storms and floods.
It says much less about vulnerability. If more people build homes in low-lying locations near the River Thames in London or in flood-prone New Orleans in the United States, then vulnerability increases. In that case, storm disasters are likely to increase, irrespective of how climate change affects storms.
Similarly, decades of scientific research show how engineering rivers for flood "control" tends to increase flood damage over the long-term. It is poor planning, rather than climate change, that is largely responsible for the resulting disasters.
Climate change's influence is often overemphasized even on the hazard side of risks. Variation in climate patterns has long existed, with cycles of various kinds running from every few years to every few decades or centuries.
Scientists are doing their best to separate long-term climate change trends from normal climate trends and variability. That is not always easy, especially at the local level.
Climate-related hazards can include cold waves, avalanches, and rainfall-related landslides. It is the myriad of detailed factors at global, regional, and local levels that determine whether such hazards will increase or decrease as a result of climate change.
For example, for a landslide to occur, material needs to be available to slide down a hill. That material takes time to build up on the slope. If more rainfall increases the frequency of landslides, then the amount of material available for each landslide could decrease, reducing the risks.
PROBLEMS WITH STATISTICS
Another problem is that long-term hazard statistics are not always reliable. Over the past decades and centuries, monitoring of hazards has become much better. Seeking trends in hazard datasets built over wide areas and over decades can be challenging.
None of this diminishes the importance or urgency of dealing with climate change. It simply says that in our assessment of the hazards and risks associated with climate disasters, we need to be scientific and be honest.
We need to say what we know and what we do not know. Where climate change clearly causes problems, we need to say that - and there is plenty to say. Otherwise, we need to admit uncertainty or a lack of data.
Given the extensive scientific evidence showing that climate change is happening and showing the need to adopt countermeasures now, why embellish climate change's influence? It is dramatic enough without the need to exaggerate.
Ilan Kelman is a senior research fellow at the Center for International Climate and Environmental Research in Oslo.
