Short answers, pulled from the story.
Over 85 percent of wildfires in the United States are started by human activity. Sources include equipment sparks, overhead power lines, campfires, and arson, with arson accounting for more than 20 percent of human-caused fires.
Wildfires can move as fast as 10.8 kilometers per hour in forests and 22 kilometers per hour in grasslands. In Australian bushfires, spot fires ignited by airborne embers have been recorded as far as 20 kilometers from the main fire front.
Forest fires in Indonesia in 1997 alone were estimated to have released between 0.81 and 2.57 gigatonnes of CO2, equivalent to 13-40 percent of annual global CO2 emissions from fossil fuels. In June and July 2019, Arctic fires emitted more than 140 megatons of carbon dioxide.
An estimated 339,000 people die each year worldwide from the effects of wildfire smoke. Wildfire smoke already contributes to nearly 16,000 annual deaths from cardiovascular and respiratory conditions, a figure projected to rise to 30,000 by 2050.
Wildfire smoke contains fine particulate matter, carbon monoxide, benzene, formaldehyde, and nitrogen oxides. Inhalation causes cardiovascular and respiratory illness, asthma exacerbation, and in the 2018 Camp Fire, lead levels near Chico increased by around 50 times in the hours following the fire.
A study published in Science Advances found that from 1975 to 2024, annual potential burning hours for wildfires in North America rose 36 percent. Climate-driven weakening of day-night weather constraints is a key factor in this increase.