Due to El Niño and global warming, 2015 natural disasters are much less costly than expected, according to a study by an insurance industry group. The insurance industry’s largest losses in recent years are due to severe winter weather. Global warming and El Niño — a weather event that warms up ocean temperatures in South America, causing the United states to get unusually warm for a year — abated these insurance costs, according to Munich Reinsurance America, Inc.