David Whitehouse writes at NetZeroWatch New study confirms Sun/Cosmic-Ray climate connection. Excerpts in italics with my bolds.

A new study published in Nature Scientific Reports by researchers at the Danish National Space Institute at the Technical University of Denmark (DTU) and The Hebrew University of Jerusalem suggests that the Sun’s activity in screening cosmic rays affects clouds and, ultimately, the Earth’s energy budget with concomitant climatic effects.

Eruptions on the Sun screen the Earth from galactic cosmic rays – energetic particles raining down on our planet from exploded stars. “The Sun carries out fantastic natural experiments that allow us to test our ideas about cosmic ray effects on the atmosphere,” professor Henrik Svensmark, lead author of the study told the GWPF.

Solar explosions produce magnetised gas that sweeps past the Earth reducing the cosmic ray flux reaching us. These events are called Forbush decreases taking their name from the American physicist Scott E. Forbush, who first noticed them more than 80 years ago. They lead to a temporarily lower production of small aerosols – molecular clusters in the air – that normally grow to seed the water droplets of low-level clouds. This, in turn, reduces the cloud cover which is known to affect climate.

The recent breakthrough is that the effect on the Earth’s energy budget has been quantified using satellite observations from the CERES instrument on NASA’s Terra and Aqua satellites.

The observational data indicate that the Earth absorbs almost 2 Watts per square metre additional energy within 4 to 6 days of the cosmic-ray minimum. Such a large effect is a major surprise since the general consensus of the climate community, recently expressed in the 2021 released IPCC report AR6 (chapter 7.3.4.5), is that, “… the GCR [galactic cosmic rays] effect on CCN [cloud condensation nuclei] is too weak to have any detectable effect on climate and no robust association was found between GCR and cloudiness. … There is high confidence that GCRs contribute a negligible ERF [effective radiative forcing] over the period 1750 to 2019.”

These new results show the IPCC’s conclusion will need to be reassessed. Two Watts per square metre can be compared with the IPCC report’s estimate of solar effective radiative forcing over the period 1750 to 2019 of only 0.01 Watts per square metre (obtained by only considering solar irradiance changes).

“We now have simultaneous observations of decreases cosmic rays, aerosols, clouds, and the energy budget” says professor Nir Shaviv.

Background from previous post The Cosmoclimatology theory 

An article at GWPF provides a concise description linking solar activity to earth’s climate. It pulls together several strands of observations and thought presented in recent posts, which are referenced at the end.

The GWPF article (here) is from Deepak Lal and focuses on why India should follow the US out of the Paris accord, but I am more interested in the scientific rationale. The author nicely summarizes an alternative explanation for climate fluctuations to that of IPCC “consensus” scientists. Excerpts below with my bolds.

Propounded by Danish physicist Henrik Svensmark and his associates, the cosmoclimatology theory states that climate is controlled by low cloud cover, which when widespread has a cooling effect by reflecting solar energy back into space and vice versa. These low clouds, in turn, are formed when sub-atomic particles called cosmic rays, emitted by exploding stars, combine with water vapour rising from the oceans.

The constant bombardment of the planet by cosmic rays is modulated by the solar wind, which when it is blowing prevents cosmic rays from reaching the earth and creating low clouds. The solar wind in turn is caused by the varying sunspot activity of the sun.

When, as recently, sunspot activity decreases we get the global ‘cooling’ observed during the recent ‘pause’ in global warming. Furthermore, as noted by the Princeton physicist William Happer (see my column “Clouds of Climate Change”, September 2011), the millennial ‘ice core’ records of the correlation between CO2 and temperature show “that changes in temperature preceded changes in CO2 levels, so that CO2 levels were an effect of temperature changes.

Much of this was probably due to outgassing of CO2 from the warming oceans or the reverse in cooling” (“The truth about greenhouse gasses”). For the oceans are the primary sinks as well as emitters of CO2. Given their vastness relative to the earth’s surface, it takes a long time for the ocean to warm from rises in terrestrial temperatures (and vice versa), hence the lag between temperature and CO2 levels.

The missing piece in the cosmoclimatology theory was the physical link between cosmic rays and cloud formation. The first confirmation of the basic hypothesis that “ions [cosmic rays] are fundamental for the nucleation of aerosols [tiny liquid or solid particles that provide a nucleus around which droplets can form from water vapour in the air]” was confirmed by the CLOUD experiment at CERN — the particle physics laboratory in 2011. (See Kirby et al, Nature, (2011), 476, 429-433: Cloud formation may be linked to cosmic rays  Experiment probes connection between climate change and radiation bombarding the atmosphere.

But there was still a problem with the hypothesis. It was that, even if as the CLOUD experiment showed ions helped aerosols to form and become stable against evaporation — a process called nucleation — these small aerosols “need to grow nearly a million times in mass in order to have an effect on cloud formation.”

The latest research by Svensmark and his associates (reported in H Svensmark et al. “Increased ionisation supports growth of aerosols into cloud condensation nuclei” Nature Communications 2017;8(1) shows“ both theoretically and empirically and experimentally, how interactions between ions and aerosols can accelerate the growth by adding material to the small aerosols and thereby help them survive to become cloud condensation nuclei” (David Whitehouse: “Cosmic Rays Climate Link Found”). This implies, Prof Svensmark argues, that the effect of the sun on climate could be “5-7 times stronger than that estimated due to changes in the radiant output of the sun alone.”

It also explains why over geological time, there have been much larger variations in climate correlated with changes in cosmic rays. He adds that “it also negates the idea that carbon dioxide has been controlling the climate on the se timescales. ”Thus, the Medieval Warm period around 1000 AD and the subsequent Little Ice Age between 1300AD and 1900AD fit with changes in solar activity.

It also explains climate change observed over the 20th century. Similarly, coolings and warmings around 2 degrees Celsius have occurred repeatedly over the last 10,000 years with variations in the Sun’s activity and cosmic ray influx. While over longer time periods there are much larger variations of up to 10 degrees Celsius as “the Sun and Earth travel through the Galaxy visiting regions with varying numbers of exploding stars”. Svensmark concludes that ‘finally we have the last piece of the puzzle explaining how particles from space affect climate on Earth. It gives an understanding of how changes caused by solar activity or by supernova activity can change climate”.

Surely with this confirmation of the cosmo-climatology theory a Nobel Prize in physics for Svensmark and his associates cannot be far off, and with that the end of the hubristic theory of anthropogenic CO2 generated climate change.

Last word to Svensmark from his December 2017 publication

The missing link between exploding stars, clouds, and climate on Earth  Breakthrough in understanding of how cosmic rays from supernovae can influence Earth’s cloud cover and thereby climate

Summary: The study reveals how atmospheric ions, produced by the energetic cosmic rays raining down through the atmosphere, helps the growth and formation of cloud condensation nuclei — the seeds necessary for forming clouds in the atmosphere.

Cosmic rays interacting with the Earth’s atmosphere producing ions that helps turn small aerosols into cloud condensation nuclei — seeds on which liquid water droplets form to make clouds. A proton with energy of 100 GeV interact at the top of the atmosphere and produces a cascade of secondary particles who ionize molecules when traveling through the air. One 100 GeV proton hits every m2 at the top of the atmosphere every second.

The hypothesis in a nutshell

• Cosmic rays, high-energy particles raining down from exploded stars, knock electrons out of air molecules. This produces ions, that is, positive and negative molecules in the atmosphere.
• The ions help aerosols — clusters of mainly sulphuric acid and water molecules — to form and become stable against evaporation. This process is called nucleation. The small aerosols need to grow nearly a million times in mass in order to have an effect on clouds.
• The second role of ions is that they accelerate the growth of the small aerosols into cloud condensation nuclei — seeds on which liquid water droplets form to make clouds. The more ions the more aerosols become cloud condensation nuclei. It is this second property of ions which is the new result published in Nature Communications.
• Low clouds made with liquid water droplets cool the Earth’s surface.
• Variations in the Sun’s magnetic activity alter the influx of cosmic rays to the Earth.
• When the Sun is lazy, magnetically speaking, there are more cosmic rays and more low clouds, and the world is cooler.
• When the Sun is active fewer cosmic rays reach the Earth and, with fewer low clouds, the world warms up.

Update October 2021

Additional Resources:

Nature’s Sunscreen

Magnetic Pole Swapping and Cooling

Autumnal Climate Change