\nWe summarize the week’s scientific breakthroughs every Thursday.<\/p>\n
input[type=”radio”].svelte-wecxzz{display:none}.payment-option-wrapper.svelte-wecxzz.svelte-wecxzz{display:flex;flex:1 0 28%;width:100%}.payment-option-wrapper.svelte-wecxzz.svelte-wecxzz:only-child{max-width:325px}.box-container.svelte-wecxzz.svelte-wecxzz{display:flex;flex-direction:column;flex:1 1 0;width:0;text-align:center}.inner-box.svelte-wecxzz.svelte-wecxzz{border:var(–zf-payment-options-border);border-radius:var(–zf-payment-options-borderRadius);background-color:var(–zf-payment-options-bgColor);height:100%;display:flex;flex-direction:column}.box-container.highlighted.svelte-wecxzz .inner-box.svelte-wecxzz{border-top-left-radius:0;border-top-right-radius:0}.box-container.svelte-wecxzz .box-content.svelte-wecxzz{flex-grow:1;padding:30px 20px;margin:0 10px;overflow:hidden}.box-container.svelte-wecxzz .styled-box-content.svelte-wecxzz{color:var(–zephr-color-text-main);font-family:var(–zf-root-fontFamily)}
What\u2019s behind the rise in extreme fires in North America? Here are three sometimes counterintuitive facts about boreal fires that might help pierce through the haze.<\/p>\n
Lightning sparks the biggest fires<\/h2>\n The recipe for an extreme wildfire consists of three ingredients: an ignition source; dry vegetation that\u2019s primed to burn; and hot, windy weather.<\/p>\n
Fires in Canada\u2019s boreal forests are primarily ignited by lightning or by human activities: the careless toss of a cigarette butt, a stray ember from a bonfire or a spark from a railway. In terms of the simple number of fires they start each year, lightning and humans are roughly on a par.\u00a0<\/p>\n
But when it comes to total area burned, it\u2019s not even close. Lightning is by far the primary ignition source, responsible for an estimated 92 percent of area burned \u2014 often in Canada\u2019s remotest regions, where fires tend to be monitored rather than fought.<\/p>\n
\u201cThe boreal forest is evolved to burn; that\u2019s how it replaces itself,\u201d says Chelene Hanes, a wildland fire scientist with the Canadian Forest Service who is based in Sault Ste. Marie in Ontario. \u201cIt\u2019s ecologically responsible to let fires do what they do,\u201d as long as they\u2019re not threatening to impact communities, she says.<\/p>\nWildfire that ignited around July 13 in northwestern Ontario, Canada, blazed through Collins First Nation, an Ojibwa community, shown here on July 22.<\/span>Chris Young\/The Canadian Press via AP<\/span><\/figcaption><\/figure>\nCanada is so vast and sparsely inhabited that fighting fires in its uninhabited wilderness is also not a good use of resources. Effective fire suppression typically requires quick response for maximum effectiveness, perhaps within the first 30 minutes after ignition. That\u2019s far less possible for remote fires than for those in populated areas.<\/p>\n
Public messaging about fire management probably contributed to a decline<\/a> in human-caused fires by 2018. But recent data suggest that human-caused fires are again on the rise. That may not be because people have become more careless, Hanes says. Instead, as global climate change increasingly makes the landscape drier and hotter, even smaller sparks could lead to massive blazes.\u00a0<\/p>\n