The image shows the trend of vapor pressure deficit over the Amazon rainforest during the dry season months — August through October — from 1987 to 2016. The measurements are shown in millibars — a standard unit of measure for atmospheric pressure. Vapor pressure deficit is the ratio of how much moisture is present in the atmosphere compared to how much moisture the atmosphere can hold. The trend shows the decline of moisture in the air, particularly across the south and southeastern Amazon, which is caused by a combination of human activities, including changes in land use, forest burning and its byproduct, black carbon, along with activities that have increased carbon monoxide and carbon dioxide levels in the region.