Cloud Forcing - a.k.a. Cloud Radiative Forcing (CRF) or Cloud Radiative Effect (CRE) - refers to the complex effects that cloud cover has on the Earth's 'radiation budget' - in other words how much clouds affect global warming by the Sun.

At present, it's not known, on a global scale, whether everyday cloud-cover tends to decrease or increase global warming. This uncertainty has profound implications for climatologists attempting to create accurate computer models of Climate Change.

Clouds can reflect heat-inducing radiation from the Sun back into space, but can also increase atmospheric heating due to absorption of radiation coming from below (radiating from the Earth's surface).

Some current calculations and climate models tend to assume that, on average, clouds might be causing cooling of the Earth's surface by about 13 W/m².

But, because of the extreme complexity of climatic heating/cooling feedback loops, there is considerable disagreement amongst climatologists about their overall effects.

Clouds remain one of the largest uncertainties in future projections of climate change by global climate models, owing to the physical complexity of cloud processes and the small scale of individual clouds relative to the size of the model computational grid."

Source : Wikipedia

Various Earth orbiting satellites (e.g. GERB - see link below) are part of current studies aimed at resolving the questions of clouds' effects on Climate Change.

However :

These effects collectively referred to as Cloud Forcing or Cloud Radiative Forcing (CRF) and Feedback are not yet understood to the level where it can be predicted with certainty whether their possible feedbacks will in total be positive and accelerate, or negative and slow down global warming."

Source : Wikipedia

Also see : Aviation contrails (climate impact)plugin-autotooltip__plain plugin-autotooltip_bigAviation contrails (climate impact)

Jet engines used in commercial and military aircraft typically burn carbon-based fuels (e.g. kerosene). When the fuel burns, a by-product is CO2, which is a potent greenhouse gas and contributes towards global warming.