It is estimated that clouds globally contribute to cooling for 17 W per square meter. However to calculate the real contribution we should know not only the cloud coverage, but also the microphysical characteristic of each cloud (phase, water or ice, DSD, shape of ice crystals) their elevation, eventual superposition of different cloud types, their 3D shape (normally are simuated as slabs in the models). Moreover the contribution of secondary scattering is very difficult to calculate. In summary the effect of clouds is very poorly simulated in the IPCC climate models and this is the main reason for me to reject the model conclusions as reliable forecast of future climate, rather I consider them as simply scenarios. No doubt that an anthropogenic effect on cloud microphysics exists, direct (on radiation transfer) and indirect (on aerosols acting as CCN or IN). This effect is difficult to calculte and this is reducing the reliability of IPCC cimate models. Franco Prodi

Dr Franco Prodi thank you for your contribution to the discussion

Thinning of cirrus clouds could be achieved by injecting ice nuclei (such as dust) into regions where cirrus clouds form, making the ice crystals bigger and reducing the cirrus optical depth. Thinning of the clouds could allow more heat to escape into space, thereby cooling the planet. Cirrus Cloud Thinning is a solar geoengineering proposal which aims to eliminate or thin cirrus clouds to allow heat to escape into space. Seeding decreases the frequency of the most extreme precipitation globally. However, the extreme precipitation events occur more frequently in the Sahel and Central America, following the mean precipitation increase due to a northward shift of the Intertropical Convergence Zone.Clouds play an important role in both warming and cooling our planet. Clouds give us a cooler climate on Earth than we would enjoy without clouds. However, as Earth's climate warms, we won't always be able to count on this cooling effect. At any given moment, about two-thirds of our planet is covered by clouds. Essentially, all clouds are reflective and create a cooling effect on the climate, but some are also very good at trapping heat, acting as a blanket across the planet and helping to warm it further. So some clouds decrease global warming, while others increase it. Clouds can trap that heat from the Sun. At night, when there's no sunlight, clouds are still trapping heat. It's sort of like clouds are wrapping Earth in a big, warm blanket. So clouds can have both a cooling effect and a warming effect. They carry solar energy from the warm tropics to other parts of the globe through weather systems. But they also act as gatekeepers between Earth and space, helping regulate the global temperature by capturing and releasing infrared (thermal) energy in the atmosphere. In this respect, clouds are like greenhouse gases. Because a cloud usually has a higher albedo than the surface beneath it, the cloud reflects more shortwave radiation back to space than the surface would in the absence of the cloud, thus leaving less solar energy available to heat the surface and atmosphere. Clouds warm or cool Earth's atmosphere by absorbing heat emitted from the surface and radiating it to space. Clouds warm and dry Earth's atmosphere and supply water to the surface by forming precipitation. Therefore, thinning or removing these clouds would reduce their heat trapping capacity, resulting in a cooling effect on Earth's climate. This could be a potential tool to reduce anthropogenic global warming. Some clouds contribute to cooling by reflecting part of the Sun's energy back into space. Others contribute to warming by acting like a blanket and trapping some of the energy of Earth's surface, amplifying the greenhouse effect.

Daily cloud seeding like the Saudis are doing right now. The satellite image from April 29 to show the results.

Dr Craig Carlton Dremann thank you for your contribution to the discussion