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 Earth has a natural greenhouse effect where certain gases (known as greenhouse gases) in the atmosphere allow the sunlight to enter but absorb the heat radiation.Because these gases absorb the heat, they keep the average surface temperature on Earth around 14Â°C.ince the industrial revolution, human activity has increased the amount of greenhouse gases in the atmosphere (shown in the graph to the right). The increased amount of gases which absorb heat, has directly lead to more heat being retained in the atmosphere and thus an increase in global average surface temperatures.