Climate change indicators: High and Low temperatures

What does the temperature indicator track?

Trends in unusually hot and cold temperatures across the contiguous U.S.

What data source is used for the temperature indicator?

NOAA weather stations.

When are unusually hot summer temperatures measured?

During June through August, using daily highs and lows.

What trend has been observed in hot summer temperatures since the 1970s?

Increasing frequency, especially of hot nights.

Why are hotter nights concerning?

They reduce nighttime cooling, increasing health and energy risks.

Which U.S. regions have seen an increase in unusually hot days?

Western U.S., Gulf Coast, and Atlantic Coast.

Which region has seen a decrease in unusually hot days?

Central U.S.

When are unusually cold temperatures measured?

From December through February.

What trend has been observed in cold winter temperatures since the 1980s?

A sharp decline in unusually cold days and nights.

Which U.S. region has seen the largest decrease in cold extremes?

Western U.S.

How have record high and low temperatures changed since the 1970s?

Record highs have become more frequent than record lows.

What does a higher number of record highs indicate?

A warming trend in daily weather extremes.

How did record highs compare to record lows from 2000–2009?

There were twice as many record highs as lows.

Why does this matter for public health?

Heat stress increases, especially during warm nights.

How does temperature change impact agriculture?

Crops and livestock are vulnerable to both heat and cold.

How does climate change affect energy use?

Higher temperatures increase demand for air conditioning; cold increases heating fuel use.

How does temperature variability affect infrastructure?

Extreme temperatures strain power grids and other systems.

Are these trends consistent with global warming models?

Yes, they support the expected patterns of climate change.

What is the heat index?

A measure combining temperature and humidity to describe perceived heat.

What is the albedo effect?

The reflectivity of a surface, affecting how much solar energy is absorbed.

How are “unusual” hot and cold days defined?

Days with temperatures in the top or bottom 10% of the historical record.

What are the main data networks used for temperature indicators?

U.S. Climate Extremes Index, U.S. Historical Climatology Network, and Global Historical Climatology Network.