“Why would anyone expect carbon dioxide, a gas that represents 400 parts per million of all atmospheric gases, barely 0.04% of all atmospheric gases to have the capacity to affect something as huge and dynamic as the weather or climate?”
This is an oft repeated question and requires an answer, and I shall give you my answer, but first we have to define our terms. The atmosphere varies from place to place and according to altitude. Parts of its upper region increase in heat with altitude; parts of its lower region decrease in heat in altitude. Its middle region is heated by light from the sun; its lower region is heated by light reflected back from the earth (mainly).
So we have to understand that atmospheric gases exist in different quantities in different parts of the atmosphere. Generally, the higher you go the thinner the atmosphere.
It is generally accepted science that carbon dioxide is a greenhouse gas; the question I quoted at the beginning of this essay accepts that carbon dioxide is a greenhouse gas, but queries how minute quantities can affect our climate. It is accepted by science that water vapour is also a greenhouse gas. Water vapour currently comprises an average of around 0.25% of the atmosphere at lowest level of the atmosphere (the troposphere) but varies from place to place from virtually nothing to a maximum of 4%.
Carbon dioxide also varies from place to place. The ocean contains about twenty times more carbon dioxide than the atmosphere.
By itself carbon dioxide might have a very slight warming effect if more carbon dioxide is created from fossil fuel burning than the planet can recycle. However, any temperature of the planet makes more water evaporate and become vapour. Water vapour is a greenhouse gas, and this additional water vapour causes the temperature to go up even further.
Generally studies conclude that if additional carbon dioxide in the atmosphere should cause of a warming of 1°C that warming will increase water vapour in the atmosphere which will create a further warming of probably more than an additional 1°C. It is similar to “buy one get one free”.
Of course, the warming is not uniform across the planet and the way that heat moves from warm places to cooler places, pushed along by air and ocean oscillations means that some places will get warmer while others may get cooler. What seems to be happening in the last ten or so years is that most places on land have warmed very slightly, but the oceans in most places have warmed more considerably.
In any event the answer to the question is a simple yes, and the explanation for the answer is not beyond simple understanding.