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 net effect of clouds on the climate today is to cool the surface by about 5Â°C (9Â°F). One can calculate that a higher surface temperature would result from the buildup of greenhouse gases in the atmosphere and the consequent slowing of heat radiation from the surface, provided nothing else changes.