Thursday, 12 November 2020

Climate Solutions are Possible!

This post is about an excellent climate modelling tool called En-ROADS,  developed by MIT and other organisations.  By using a "hands-on" approach, it allows individuals or groups to learn about those factors producing climate change and also how to best to address the climate crisis.  I haven't included any sample graphics - it's better if you explore the link above. You might start with the 3 minute video demo of how it works, then try running your own model.

This is what I like about En-ROADS:  

  • Tackling climate change is tricky. Leaving aside factors such as the influence of vested interests and biased media, climate modelling requires physical, economic and social models, with a high degree of interaction between the parameters. For example, given a price per ton on carbon, how will this affect CO2 emissions and then what is the impact on mean temperature over future decades?   How does this strategy compare to (say) a tax of coal?   En-ROADS actually answers these questions, plus a great deal more.  
  • Are the models accurate?  It's reassuring that En-ROADS has been compared to many other climate models and IPCC standard scenarios (called SSPs) - it seems to give quite consistent results.  There's a lot of good climate science behind the software, and it's being regularly updated. 
  • This tool is freely accessible to the public via a simple http web page.  With so many input and output parameters the user interface it critical.  En-ROADS provides a set of the most important adjustment levers (eg adjust how much of the transport system is electrified, assume a higher or lower population growth, adjust taxes on oil etc) then shows the resultant effect on mean temperature increase, compared to "business as usual".  However there's a wealth of other results that can be displayed, plus detailed settings that can be adjusted.  This degree of transparency and detailed modelling is wonderful - it's necessary to capture the complexity, but also might be daunting for casual users.   En-ROADS therefore suggests a guided approach eg in an interactive workshop format.  

Is En-ROADS perfect?  It's scope is already very broad, so it's not surprising that some aspects can not be included.  For example
  • A global, rather than regional, model is assumed so it represents a global mean of climate policies and their results.  Note some other tools on the Climate Interactive site look into various regional issues. 
  • In general, tipping points are hard to model, plus the interaction between these positive feedback loops.   Thus in some respects En-ROADS may be too optimistic, depending on the values of various assumptions used in the model.  At least En-ROADS provides useful information, plus references,  regarding its assumptions.  
  • En-ROADS predicts outcomes such as CO2 concentrations over time, sea level rise, mean temperature increase etc.  The "business as usual" path shows over 2 degrees temperature rise by mid century and about 4 degrees by 2100.  Of course 4 degrees will probably result in catastrophic outcomes for humanity.  At present it's too hard to model the effect of this on (say) GDP. 

En-ROADS allows users to explore climate mitigation strategies in order to understand drivers and discover the most promising approaches.   It's well designed and implemented, with a lot of detailed information if users want to explore specific areas.  It also includes many examples and includes a focus on equitable carbon-neutral transformations.  

En-ROADS suggests it's possible to avoid a climate disaster via a suitable mix of strategies.  However it's not easy to achieve (say) less than two degrees average temperature rise and there's certainly no single quick fix.  


"Dealing with Climate Change" U3A Workshop:   May 2021   

Wednesday, 7 October 2020

Checking on the Bee Hive

Temperature, humidity and other parameters of bee hives can be measured and provide useful indications of hive status and health.   Here is one example of commercially-available equipment.   

So during the last year I've been monitoring our bee hive.  A Lora system sends telemetry from Arduino-based electronics next to the hive.  Over the last Spring and Summer the temperature regulation was extremely good - usually within one degree, whatever the weather.  During Winter the temperature was highly variable and we wondered if the hive was healthy.  The Adelaide plains are fairly easy for bees during colder months and in previous Winters we left the Super on the Brood Box, however this year we removed the Super and I added extra insulation.  Happily the bee hive looked OK during some physical inspections. 

Hive Temp at end of August 

We didn't need to worry.  The plot shows temperature near the middle of the Brood Box in green, plus external temperature in black, over a one week period. Towards the end of this period the variations seem to decrease and the average temperature is rising.  

Hive Temperature, start of September  

This graph follows directly from the previous.  (My simple plotting doesn't restart the day number partway through the plot, but it's the first week of September.) Amazingly the bees have begun to closely regulate the brood temperature!   From this research,  

Honeybee larvae and pupae are extremely stenothermic, i.e. they strongly depend on accurate regulation of brood nest temperature for proper development (33–36°C).

It seems remarkable that bees can do this.  As warm-blooded mammals we can regulate temperature pretty well. But the bees are doing this for their nursery area, using both active and passive methods.  Furthermore they can turn it on or off.  They don't waste energy in thermoregulation unless there are young bees to look after.  Spring is a busy time in the bee hive!   

Apart from temperature,  we've also looked at humidity in the hive. Thermistors are easy to insert into the hive compared to humidity sensors.  For a more novel experiment, I've tried to measure the level of hive activity.  Last year our hive swarmed a few times.  We managed to capture the swarms and donate them to worthy recipients, but swarming may not be ideal for the neighbours.  So it seems useful to at least know if the hive is more active than usual.  Others have used audio and even video processing methods.  I've tried sensing the bee motion in and out of the hive via light-level variations.    Light Dependent Resistors (LDRs) at either end of the hive entrance measure the instantaneous light levels, which change as bees walk by. The figure below shows typical results over 7 days.  

Hive Activity over one week

The upper plot shows the mean light level on a log scale.   LDRs have terrific dynamic range and during the dark periods (i.e. nights) they even pick up moon light!   The lower plot shows the normalised standard deviation over intervals of about 20 seconds.  The two sensors at each end of the entrance gives rise to blue and green plots, although the green is largely over-written.  You can see that bee activity varies quite a bit from day to day, as the weather changes.  Perhaps the next step will be a temperature compensated plot that provides alerts on unusual activity.  

The activity monitoring started in Winter but the LDRs had minimal protection and failed after a few months. Close inspection shows moisture ingress on the sensor surface.   The encapsulation of LDR devices probably varies considerably.  I'm hoping my current LDRs will last longer - each is encased in the end of a glass test tube to provide more protection. This image shows one end of the bridge over the hive entrance, before installation.  The upper surface sits next to the side of the hive.  

Wednesday, 1 July 2020

21cm Radio Astronomy

The image above shows recent results from our 2m dish in Prospect looking at the 21 cm Hydrogen signal (with star positions superimposed).  It's plotted in galactic coordinates and represents data collected over a few months.  Red indicates H1 moving away from us; blue is Doppler shifted to higher frequencies as the H1 moves towards us.  Leaving the dish in a fixed position for one day gives a curved track as the Earth rotates. (For example the almost circular tracks in the slightly-lower right side arose when the antenna was close to the South Celestial Pole.  The Pointers and Southern Cross can be clearly seen near zero latitude.)     We did a talk on this project recently for AREG

Thursday, 9 January 2020

Sun Shades to Cool the Earth?


Given the present inadequate global response to reducing greenhouse gas (GHG) emissions, some people are considering geoengineering options to ameliorate the effects of the climate changes which we have begun to observe.  Many worry that deliberate intervention in the Earth's climate system is a bad idea since the unexpected effects could be dangerous and in addition the usual fossil fuel polluters might use this solution as a "get out of gaol" card.  The top priority should be drastic GHG reduction, but it seems prudent to explore the feasibility of geoengineering methods as backup.  Hence this page briefly reviews the idea of reducing global warming by a space-based approach of solar flux reduction.   See [1] or [2] for an introduction to geoengineering. 

Solar Flux Control 
The idea of controlling solar radiation to limit climate change effects is not new (e.g. see [3]).  Terrestrial methods of geoengineering may be cheaper, but this space-based approach has potential advantages:

  • once installed, it might be possible to adjust the attenuation fairly rapidly
  • it might offer some ability for varying the solar radiation depending on latitude.  
The figure below contains a simple 2D model of flux attenuator located near the L1 Lagrange point, a distance (L in the figure) about 1.5 million km from the Earth on the left hand side.  At this location the gravitational forces towards the Earth and the Sun are balanced, providing a pseudo-stable "parking spot".   The sun's disc is shown in the right;   it subtends an angle of about half a degree from the Earth.  We assume some type of mirror is used to block solar radiation that would otherwise fall on the Earth's surface.  (Other options such as a large thin Fresnel lens to disperse sunlight have also been proposed.)  

Fig 1:  2D Model of Solar Flux Control (not to scale) 

For realistic mirror dimensions, no part of the Earth would be fully in shadow from the mirror (i.e. the umbra doesn't extend to the earth).  An observer on Earth would not notice any change in the Sun, unless equipped with a pin-hole camera or similar. Assume that the mirror's position  can be adjusted in the vertical direction shown in Fig 1.  This allows some scope in varying the flux versus latitude on the Earth.   For example a simple evaluation using the 2D model above, with a 1000 km mirror, offset by 3000km, gives the Figure 2 reduction in flux versus position on the Earth.  In this example case the mirror is located "below" the Earth-Sun midpoint so for regions near the North Pole, no part of the Sun's disc is obstructed and the attenuation is zero.   

Fig. 2: Example of Solar Flux Reduction 
Previous studies of similar sun shades have concluded that only a few percent reduction in solar radiation might counter the GHG heating effects and have suggested mirrors of similar dimensions.  

Radiation will exert a force on the mirror (solar sails use this  effect) and for (say) a 1000 km square mirror this is large (e.g. almost 8 million Newtons). However this should not pose a major problem as the structure can be placed on the Sun side of the L1 Lagrange point such that the radiation force balances the net gravitational force.  Of course second-order effects would require an active positioning system, probably provided by many small thrusters.  

The main challenge appears to be manufacture and transport of the mirror(s).  For a mirror of 1 gram per square meter, the area mentioned above requires 1 million tonnes of mirror.  Fabrication on the Earth  doesn't appear to be likely given estimates of the total mass launched into space are considerably less.   Manufacture in space seems more promising but is probably a long term project compared to the time available.  For example the moon contains a large percentage of Aluminium that might form the bulk of the reflecting material.  Some asteroids could also provide useful raw materials, such as Nickel.  If significant amounts of Aluminium could be mined and smelted on the Lunar surface, it could be used to make very thin reflecting sheets (possibly unrolled and assembled at L1) together with structural elements required for the large fleet of positioning cubesats.  Presumably the required micro-electronic components could be made on Earth, with highly automated assembly of the cubesats on the Moon and possible launch via a Space Gun


Control of solar flux seems feasible but is a long term project.  All the more reason to make rapid cuts in our greenhouse gas emissions and avoid the need for these extreme measures.