Claim: Globally averaged thermometers show two periods of warming since 1900: a half-degree from natural causes in the first half of the 20th century, before there was an increase in industrial carbon dioxide that was enough to produce it, and another half-degree in the last quarter of the century.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: The average global temperature on Earth has increased by about 0.8° Celsius (1.4° Fahrenheit) since 1880; Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20 °C per decade.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: One argument is that of global warming occurring due to human-caused emission of greenhouse gases, particularly carbon dioxide produced by the burning of fossil fuels.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: Increases in atmospheric concentrations of CO 2 and other long-lived greenhouse gases such as methane, nitrous oxide and ozone have correspondingly strengthened their absorption and emission of infrared radiation, causing the rise in average global temperature since the mid-20th century.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: Since the Industrial Revolution anthropogenic emissions – primarily from use of fossil fuels and deforestation – have rapidly increased its concentration in the atmosphere, leading to global warming.

Relevance (1 = gold evidence, 0 = mined hard negative): 1
Passage: Before the Industrial Revolution, naturally occurring amounts of greenhouse gases caused the air near the surface to be warmer by about 33 °C (59 °F) than it would be in their absence.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: Climate proxy records show that natural variations offset the early effects of the Industrial Revolution, so there was little net warming between the 18th century and the mid-19th century, when thermometer records began to provide global coverage.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: Global warming refers to the warming caused by human technology since the 19th century or earlier.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: Human-caused increases in greenhouse gases are responsible for most of the observed global average surface warming of roughly 0.8 °C (1.5 °F) over the past 140 years.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: The global average and combined land and ocean surface temperature, show a warming of 0.85 [0.65 to 1.06] °C, in the period 1880 to 2012, based on multiple independently produced datasets.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: IPCC AR4 WG1 Ch9 2007, p. 690: "Recent estimates indicate a relatively small combined effect of natural forcings on the global mean temperature evolution of the second half of the 20th century, with a small net cooling from the combined effects of solar and volcanic forcings."

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: The global temperature increase since the beginning of the industrial period (taken as 1750) is about 0.8 °C (1.4 °F), and the radiative forcing due to CO 2 and other long-lived greenhouse gases – mainly methane, nitrous oxide, and chlorofluorocarbons – emitted since that time is about 2.6 W/m2.

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: "Estimating Changes in Global Temperature since the Preindustrial Period".

Relevance (1 = gold evidence, 0 = mined hard negative): 0
Passage: Since the start of the 20th century, the global mean surface temperature of the Earth has increased by more than 0.7°C and the rate of warming has been largest in the last 30 years.