Another sign of Graves' disease is hyperthyroidism, i.e., overproduction of the thyroid hormones T3 and T4. Normal thyroid levels are also seen, and occasionally also hypothyroidism, which may assist in causing goitre (though it is not the cause of the Graves' disease).
Without this greenhouse effect, the average surface temperature would be 255 degrees kelvin (-18 degrees Celsius or 0 degrees Fahrenheit); a temperature so low that all water on Earth would freeze, the oceans would turn into ice and life, as we know it, would not exist.
The warm planetary surfaces then emit infrared radiation of their own. The Greenhouse effect describes the condition where this infrared radiation is trapped and absorbed by gases and vapor in the atmosphere, and the atmosphere is then heated more than it would otherwise be without the Greenhouse effect.