How could anyone possibly know that?
NBC News reports:
According to Hoerling, climate change was likely responsible for “about 3 to 5 percent” of the water vapor in the fetch of tropical moisture, given that a warmer atmosphere can hold more water and published studies indicate “a few percent increase in water vapor to date.”
The rest, he said, is due to atmospheric circulation patterns that appear inconsistent with models used to simulate the global climate, including those being examined for the upcoming report from the Intergovernmental Panel on Climate Change. Those models project a slight decline in summertime rainfall, he said.