But the extreme heat wave, and accompanying drought and wildfires, in normally cool central Russia seems to be prompting a shift in thinking.

“Everyone is talking about climate change now,” President Dmitri A. Medvedev told the Russian Security Council this month. “Unfortunately, what is happening now in our central regions is evidence of this global climate change, because we have never in our history faced such weather conditions in the past.”

Thermometer measurements show that the earth has warmed by about 1.4 degrees Fahrenheit since the Industrial Revolution, when humans began pumping enormous amounts of carbon dioxide, a heat-trapping greenhouse gas, into the atmosphere. For this January through July, average temperatures were the warmest on record, the National Oceanic and Atmospheric Administration reported Friday.

The warming has moved in fits and starts, and the cumulative increase may sound modest. But it is an average over the entire planet, representing an immense amount of added heat, and is only the beginning of a trend that most experts believe will worsen substantially.

If the earth were not warming, random variations in the weather should cause about the same number of record-breaking high temperatures and record-breaking low temperatures over a given period. But climatologists have long theorized that in a warming world, the added heat would cause more record highs and fewer record lows.

The statistics suggest that is exactly what is happening. In the United States these days, about two record highs are being set for every record low, telltale evidence that amid all the random variation of weather, the trend is toward a warmer climate.

Climate-change skeptics dispute such statistical arguments, contending that climatologists do not know enough about long-range patterns to draw definitive links between global warming and weather extremes. They cite events like the heat and drought of the 1930s as evidence that extreme weather is nothing new. Those were indeed dire heat waves, contributing to the Dust Bowl, which dislocated millions of Americans and changed the population structure of the United States.