This question needs clarifications. It could be interpreted in two ways. The first is: "Which climate forcing will make future climate events or predictions harder to model?" and the second is "Given our current understanding, which climate forcing has the most uncertain future development?".

First, the one sole factor that affects modeling is - nonstationarity. Every model has internal parameters and hyperparameters, and more-less is "trend based". Every nonlinearity (which is still not nonstationarity) and nonstationarity is a challenge. So I would not agree that it is plain "natural variations". It is just a subset of variations which cannot be modeled. Some variations can be modeled very well (e.g. Milankovitch cycles).

Now, more concretely, in "The Warming Papers: The Scientific Foundation for the Climate Change Forecast" (http://www.wiley.com/WileyCDA/WileyTitle/productCd-1405196165.html) you can find that aerosol direct and indirect forcings are most uncertain. There are many other useful infos in there. Hope this helps.

Hi Jovan,

Thank you for breaking the question into two components. The answers you provided are useful.

Dear Kenneth,

Great answer!. Thanks. The materials are useful as usual.

Dear folks,

Please read the two annexes and enlighten yourself.

Cheers,

Frank

Hello Frank,

Great resources! Thanks.

Good discussions. What's the conclusion?

Dear Asit Kumar,

It's an ongoing discussion. We are waiting for your opinion. We want you to share with ResearchGate community your wealth of specialty.

Regards

Hi folks,

As a reply to Kenneth's question for enlightenment with a short summary of the findings of the authors of Chapter 8 ( 'Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA).

I can cite the following findings from this reports executive summary:

1) Anthropogenic Forcing: It is unequivocal that anthropogenic increases in the well-mixed greenhouse gases (WMGHGs) have substantially enhanced the greenhouse effect, and the resulting forcing continues to increase. Aerosols partially offset the forcing of the WMGHGs and dominate the uncertainty associated with the total anthropogenic driving of climate change.

2) Anthropogenic Forcing: As in previous IPCC assessments, AR5 uses the radiative forcing1 (RF) concept, but it also introduces effective radiative forcing2 (ERF). The RF concept has been used for many years and in previous IPCC assessments for evaluating and comparing the strength of the various mechanisms affecting the Earth’s radiation balance and thus causing climate change. Whereas in the RF concept all surface and tropospheric conditions are kept fxed, the ERF calculations presented here allow all physical variables to respond to perturbations except for those concerning the ocean and sea ice.

3) Anthropogenic Forcing: The total anthropogenic ERF over the Industrial Era is 2.3 (1.1 to 3.3) W m². It is certain that the total anthropogenic ERF is positive. Total anthropogenic ERF has increased more rapidly since 1970 than during prior decades. The total anthropogenic ERF estimate for 2011 is 43% higher compared to the AR4 RF estimate for the year 2005 owing to reductions in estimated forcing due to aerosols but also to continued growth in greenhouse gas RF

4) Anthropogenic Forcing: Due to increased concentrations, RF from WMGHGs has increased by 0.20 (0.18 to 0.22) W m–2 (8%) since the AR4 estimate for the year 2005. The RF of WMGHG is 2.83 (2.54 to 3.12) W m–2. The majority of this change since AR4 is due to increases in the carbon dioxide (CO2) RF of nearly 10%. The Industrial Era RF for CO2 alone is 1.82 (1.63 to 2.01) W m–2, and CO2 is the component with the largest global mean RF. Over the last decade RF of CO2 has an average growth rate of 0.27 (0.24 to 0.30) W m–2 per decade. Emissions of CO2 have made the largest contribution to the increased anthropogenic forcing in every decade since the 1960s. The best estimate for ERF of WMGHG is the same as the RF but with a larger uncertainty (±20%).

5) Anthropogenic Forcing: The net forcing by WMGHGs other than CO2 shows a small increase since the AR4 estimate for the year 2005. For example a small growth in the CH4 concentration has increased its RF by 2% to an AR5 value of 0.48 (0.43 to 0.53) W m–2.

6) Anthropogenic Forcing: Ozone and stratospheric water vapour contribute substantially to RF. The total RF estimated from modelled ozone changes is 0.35 (0.15 to 0.55) W m–2, with RF due to tropospheric ozone changes of 0.40 (0.20 to 0.60) W m–2 and due to stratospheric ozone changes of –0.05 (–0.15 to +0.05) W m–2.

7) Natural Forcing: Satellite observations of total solar irradiance (TSI) changes from 1978 to 2011 show that the most recent solar cycle minimum was lower than the prior two. This very likely led to a small negative RF of –0.04 (–0.08 to 0.00) W m–2 between 1986 and 2008. The best estimate of RF due to TSI changes representative for the 1750 to 2011 period is 0.05 (to 0.10) W m–2.

8) Natural Forcing: The RF of volcanic aerosols is well understood and is greatest for a short period (~2 years) following volcanic eruptions. There have been no major volcanic eruptions since Mt Pinatubo in 1991, but several smaller eruptions have caused a RF for the years 2008–2011 of –0.11 (–0.15 to –0.08) W m–2 as compared to 1750 and –0.06 (–0.08 to –0.04) W m–2 as compared to 1999–2002. Emissions of CO2 from volcanic eruptions since 1750 have been at least 100 times smaller than anthropogenic emissions. 9) Natural Forcing: There is very high confdence that industrial-era natural forcing is a small fraction of the anthropogenic forcing except for brief periods following large volcanic eruptions. In particular, robust evidence from satellite observations of the solar irradiance and volcanic aerosols demonstrates a near-zero (–0.1 to +0.1 W m–2) change in the natural forcing compared to the anthropogenic ERF increase of 1.0 (0.7 to 1.3) W m–2 from 1980 to 2011. The natural forcing over the last 15 years has likely offset a substantial fraction (at least 30%) of the anthropogenic forcing.

These are the most important conclusions form the cited report. Let the discussion of anthropogenic versus natural forcing continue. IPCC however seems to have made up its mind. it seems to me.

Best personal regards to you all,

Frank

Dear Dr. Oyedemi,

The following literature (links/attachments) will be helpful to understand the subject (Question):

http://www.realclimate.org/index.php/archives/2005/09/what-is-a-first-order-climate-forcing/

https://www.ipcc.ch/ipccreports/tar/wg1/pdf/TAR-06.PDF

Regards

Dear Dr. Kenneth,

"..........answer to this question remains unknown since nobody can predict the path of future natural variations and they control the climate"

- this could be the conclusion (in one sentence). But, discussion may continue on the topic.

It is right that the global climate change is primarily related to the natural variations on which we have no control. The prediction through climate modeling is also not possible because of unknown factors (natural situations) controlling climate.

Regards

Hello Frank,

The findings from the executive summary are amazing. I believe the Working Group should continue to update the data as more experimental observations are added.

Hello Asit Kumar,

Super resources!

Dear Dr. Oyedemi,

The attachments are all recent publications on climate. Please go through it. You can also read the discussions on my question regarding climate. Eminent researchers have participated in the discussion. Link given below:

https://www.researchgate.net/post/Climate_change_or_global_warming-Is_it_only_due_to_anthropogenic_activities

Regards

Dear Ales Kralj,

These are recent publications. You may go through the same. Thanks.