# Recent albedo change and climate sensitivity

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The climate discussion is overwhelmingly dominated by the discussion about the influence of $CO_2$, which according the radiation transport equations describing the outgoing infrared radiation (OLR) has a certain influence on the earth’s radiation budget.

There are, however, more factors that need to be considered. **The incoming energy flux, the SW insolation, is obviously of decisive importance**. The actual amount of energy flux coming from the sun, the „solar constant“ has proven to be extremely stable, but the **global albedo, which decides how much solar flux enters the atmosphere, is an extremely important control parameter**.

The dilemma about the earth’s albedo has been, that **there is not a „nice theory“ of how to determine it from a simple (possibly human induced) cause**. On the contrary it involves many currently badly understood factors, some of which are, but others are not under human control:

- Clouds of different types at different altitudes,
- reflecting and scattering aerosols,
- influences on cloud generation, such as cosmic rays and magnetic fields,
- surface and atmospheric properties as a consequence of snow cover, urbanisation, agriculture, air pollution, etc.,
- possible feedback effects of temperature via water vapor.

Lacking a comprehensive theory, the influence of earth albedo has for a long time been neglected or ignored in the mainstream discussion.

But there is another approach. **Satellite measurements have made it possible to actually measure the direct effect of albedo on the actual solar insolation**. Recently a 30 year analysis has been published by J. Herman et al.: **Net decrease in the Earthâ€™s cloud, aerosol, and surface 340 nm reflectivity**.

This careful analysis shows a clear, significant trend for the overall reflexivity, representing 75% of the earth’s total solar insolation (latitude -60…60 degree, smaller insolation and larger albedo near the poles):

The changed reflectivity has been converted into changes of SW incoming resp. reflected flux:

This means that in the 30 years from 1980 to 2010 the solar insolation flux has increased by $2.33\frac{W}{m^2}$. **This albedo caused increase within 30 years is larger than the estimated forcing caused by the increase of $CO_2$ since the beginning of the industrialisation**.

Based on the energy balance between incoming SW insolation $S_a=S\cdot(1-a)$ and outgoing LW radiation by means of the Stefan-Boltzmann law $$T=\sqrt[4]{\frac{S\cdot(1-a)}{4\cdot\sigma}} $$ the temperature sensitivity to Insolation changes (without feedback) is $$\frac{\Delta T}{T} = 0.25\cdot\frac{\Delta S_a}{S_a} $$

$$\Delta T = 0.25\cdot \frac{2.33\cdot 255}{161.3+78} K = 0.62 K $$

During the same time of 30 years the estimated change of OLR flux due to $CO_2$ is $0.6 \frac{W}{m^2}$ resulting in the temperature sensitivity $$ \Delta T = 0.25\cdot \frac{0.6\cdot 255}{161.3+78} K = 0.16 K $$

Due to the assumed constant lapse rate the temperature change at the surface is the same as the calculated temperature change which is somewhere in the mid troposphere.

There are 2 important and simple consequences from this obervation and calculations:

**The influence of $CO_2$ accounts for 20% of the temperature change during the last 30 years, whereas the change of albedo accounts for 80% of the temperature change**.- Both forcings together would have created an average temperature change of 0.8 K. T
**he actual change of global temperature**is significantly less, depending on the institution measuring the temperature it**is 0.48..0.55 K**, which is**slightly more than half of the forcing to retain SB-balance**.**Therefore there must be rather strong negative feedback**,**which reduces the effect of additional SW flux (from albedo) resp. diminished LW flux (from $CO_2$) by appr. 50%**. The most obvious and likely „feedback“ is the buffering by heat absorption into and evaporation from the oceans, covering about 70% of the earth surface.

For the $CO_2$ sensitivity (Temperature change when doubling $CO_2$) this feedback means that** at 600 ppm we can expect a temperature change less than 0.5 degree K** compared to pre-industrial times. This conclusion is drawn under the assumption, that albedo changes are independent of $CO_2$.

Obviously the question arises, what caused the decrease of the albedo. There is no clear answer to this currently. The size of the effect and the lack of a plausible theory appear to **rule out the possibility that it is related to the global $CO_2$ level**. Currently it is more likely that there is a **causal relation of influence on cloud generation from aerosols, sun activity and cosmic rays**. But also factors of human influence through **increasing surface absorption** („urban heat islands„, desertification ) are challenges for further research and constructive activity.