 As a kid, I love to lay on my back in the grass and look up at the clouds. I would see so many crazy shapes, elephants, dinosaurs, even dragons. Climate science denialists look up at the clouds and see something even more unlikely, a challenge to the science of climate change. Unfortunately for us, it's all in their imaginations. Clouds affect the Earth's climate in many different ways, but the two most important ways are through the albedo effect and through the greenhouse effect. Albedo is a term that means how much a surface either reflects or absorbs light. In much the same way that wearing a white t-shirt will keep you cool in the summertime by reflecting sunlight, clouds reflect some of the sunlight back out to space before it can be absorbed. Thick clouds tend to have a high albedo, that is, they reflect a lot of sunlight. Putting thick white clouds between the sun and the open ocean dramatically increases the amount of sunlight that gets reflected back to space. Low thick clouds are most important for this cooling effect. By contrast, higher, thinner clouds don't reflect a lot of sunlight, but they do trap heat through the greenhouse effect. Both cloud types have a cooling albedo effect and a warming greenhouse effect, but for low clouds, the cooling effect is much stronger, and for high clouds, the warming effect is stronger. Overall, low clouds are more important, and so overall, clouds cool a lot more than they warm. But knowing how clouds affect Earth's temperature overall now doesn't tell us how clouds and their impact on climate will change as we warm the planet. If we see relatively fewer low, highly reflective clouds as we get up the ocean, we would get more warming overall. If we get relatively more low clouds, we would get less warming than we would otherwise expect. What does the available evidence tell us about how clouds will change in the future? Over the past 10 to 15 years, we've gathered enough information to be able to see how clouds change in response to changing ocean temperatures, at least over the short term. Changes in ocean temperature can occur due to natural changes in ocean cycles, such as El Nino. We can look at how these changes relate to changes in cloud cover. Overall, such changes over the past decade or so seem to point to a small warming effect, but we can't quite rule out a small cooling effect. While these studies of short-term variations are helpful for our understanding, some caution in over-interpreting their results is warranted. Longer-term temperature changes caused by greenhouse warming may affect clouds differently than short-term variations caused by El Nino. But if clouds were somehow to counteract warming, like a thermostat, this would imply that the Earth can't and hasn't warmed up very much over its history. However, we can reconstruct climate from the Earth's ancient past during hotter greenhouse periods. When we do so, we see large increases in temperature, and this rules out clouds acting like a thermostat limiting the amount of warming. Short-term observations in the present and long-term reconstructions from the past seem to be saying the same thing. Clouds won't counteract greenhouse warming. Climate models agree. On average, climate models predict a reduction in low clouds that will lead to a modest amount of additional future warming. Moreover, climate models that tend to model cloud behavior more realistically also tend to show clouds are likely to contribute more to warming in the future than models with less realistic clouds. Climate science analysts are fond of invoking cloud behavior to play down the threat of greenhouse gas emissions. They claim that as greenhouse gases increase and we start heating up, clouds will cool the Earth more, either due to an increase in low cloud cover or a reduction in high cloud cover. They claim in effect that clouds will act like a thermostat, keeping warming in check. But to claim that clouds will prevent serious global warming, climate science stylists rely on oversimplification. They act as though clouds only have an overall cooling effect. While the clouds do cool the Earth, this ignores the fact that they also warm, and that the total effect of clouds presently isn't the issue. What matters is how that effect changes, if at all, in the future. Climate science stylists then take this oversimplification and jump to a conclusion. They assume that because clouds cool now, and there is some uncertainty about their future behavior, that means clouds will act like a thermostat to prevent too much warming. To support their claims, they have cherry-picked data relying on information from records with known problems. Or in some cases, selectively choosing the start and end points within a larger data set to produce the opposite results that using the record as a whole would give. The assumption that clouds will save us is simply not warranted by the balance of evidence available to us. Our direct observations over the past decade or so suggest that the impact of clouds on future warming will be modest, and if anything, cloud changes are amplifying warming a bit. This agrees well with our most advanced climate models, which likewise suggest clouds won't cool us off, but modestly will increase warming. And we know from the climates of Earth's ancient past that there is no magical cloud thermostat that keeps the planet from heating up. Increased CO2 levels have repeatedly led to hotter climates over Earth's history.