<p>Right. We can make some estimates of the scale of the problem, but they will come with a healthy margin of error.</p>

<ul>
<li>If we assume that wood has a calorific value of 18.5 GJ/t (from the <a href="https://phyllis.nl/Browse/Standard/ECN-Phyllis" rel="nofollow noreferrer">phyllis2</a> database)</li>
<li>The area burned is 18.6 Mha (from Wikipedia <a href="https://en.wikipedia.org/wiki/2019%E2%80%9320_Australian_bushfire_season" rel="nofollow noreferrer">here</a>)</li>
<li>The standing volume of material is circa 1500 m<sup>3</sup>/ha (an educated guess based on Eucalyptus values in <a href="https://www.forestresearch.gov.uk/tools-and-resources/forest-yield/" rel="nofollow noreferrer">Forest Yield</a>)</li>
<li>The density of timber is circa 0.5t per dry m<sup>3</sup> (from <a href="https://www.forestresearch.gov.uk/research/forest-mensuration-a-handbook-for-practitioners/" rel="nofollow noreferrer">Forest mensuration handbook</a>)</li>
<li>and only 90% of that material actually burns (a guess)</li>
</ul>

<p>Then:</p>

<p>There's around 675 tonnes of material burned per ha releasing 12,150 GJ of energy which is equal to 225,990,000 TJ for the total area or 3,587,143 Hiroshima bombs (at <a href="https://en.wikipedia.org/wiki/Little_Boy" rel="nofollow noreferrer">63 TJ each</a>)...</p>

<p>This is a (very) rough calculation, but it gives a scale of the amount of heat released. This is about 10 day's worth of <a href="https://en.wikipedia.org/wiki/Solar_constant" rel="nofollow noreferrer">solar constant</a> radiation over the same area, so it might appear in local temperature readings, but bear in mind that 1) there was already unusually high temperatures in the area, and 2) fires like this produce a lot of smoke which will have had an effect on the local radiation budget.</p>

<p>In terms of all that CO<sub>2</sub>, you can expect it to be reabsorbed by the surrounding biosphere which is described in the impulse response function described in the IPCC AR5 WG1 CH8 technical supplement (<a href="https://www.ipcc.ch/site/assets/uploads/2018/07/WGI_AR5.Chap_.8_SM.pdf" rel="nofollow noreferrer">8.SM.11.1 Equations for the Global Warming Potential</a>). You can also expect the burned areas to regrow - which will absorb CO<sub>2</sub> as well. Depending on rates of growth, I would expect this to take several decades. - but there is a <em>lot</em> of very complex processes, so this is open to a lot of discussion!</p>

<p>Hope this helps.</p>

CC BY-SA 4.0
2020-02-12T10:48:45.113Z
+1 for linking back to the sources of your estimates!
samcarter_is_at_topanswers.xyz
CC BY-SA 4.0
2020-02-12T19:08:23.203Z
I feel like the most important part of this answer is buried in the middle paragraph: "This is about 10 day's worth of solar constant radiation over the same area..." So the heat generated is basically negligible in terms of global climate. I'm fairly sure that the CO2 released will have a bigger effect before it is reabsorbed, but I don't know the numbers for that.
craq
CC BY-SA 4.0
2020-02-12T20:25:51.193Z
Query regarding unit in first bullet point, should the unit GJt be GJ/t?
Fred
CC BY-SA 4.0
2020-02-12T20:43:15.043Z
It's something I learnt from other users, either here or on other SE sites. To do a superscript, bound the item to be superscripted with *<sup> ... </sup>*; i.e. for cubic meters type this: *m<sup>3</sup>*. Similarly, for subscripts used *<sub> ... </sub>*; i.e. for carbon dioxide type *CO<sub>2</sub>*. When I see someone has created some interesting formatting of text I pretend to edit the post. I then see the Matjax formatting in the text box & note it. I then cancel my pretend edit. It's a quick way of learning some interest ways to do Mathjax formatting.
Fred
CC BY-SA 4.0
2020-02-12T21:09:14.810Z
There is an easier way: just put a dollar sign to enter equation mode, then underscore _ or circumflex ^ for subscript or superscript, then the number, and finally another dollar sign to leave equation mode. If you want several numbers in a row, just put them between curly braces. It's all explained here: https://earthscience.meta.stackexchange.com/q/371/18081
Jean-Marie Prival
CC BY-SA 4.0
2020-02-13T01:52:05.997Z
@Jean-MariePrival: The $ works, but it also changes the font.
Fred
CC BY-SA 4.0
2020-02-13T03:41:46.213Z
I posted a different method of calculation below, with different sources for most things, and starting based on CO2 estimates from NASA (probably the main discrepancy?). The figures are out by 3 orders of magnitude. I'd love a review :) The things that stick out to me in your calculation as a major difference is that the burnt areas likely include a *lot* of grass land, and so the biomass/hectare is likely overestimated. Also, I think 90% figure should probably be much less than 50% in most areas - the bulk biomass in forests is in tree trunks I think, many of which do not burn.
naught101
CC BY-SA 4.0
2020-02-13T08:23:32.547Z
Given the estimates/uncertainties in the calculation saying *225,990,000 TJ* is not correct. Better would be 226 EJ.
Jan Doggen
CC BY-SA 4.0
2020-02-13T08:27:49.333Z
Fair enough, think @naught101 and I need to check each other's working in any case
Will
CC BY-SA 4.0
2020-02-12T09:49:57.067Z
2020-02-17T16:17:32.630Z
2020-02-17T16:17:32.630Z
Will
<p><strong>EDIT</strong>: As pointed out by Jean-Marie Prival and klanomath in the comments, I originally misread the specific heat of wood as per tonne, rather than per kilogram, and also used the wrong conversion between TWh and TJ.</p>

<p>Here are my rough calculations, based on CO2-release estimates from NASA:</p>

<ul>
<li>306 MtCO2 (<a href="https://en.wikipedia.org/wiki/2019%E2%80%9320_Australian_bushfire_season#Environmental_effects" rel="nofollow noreferrer">wikipedia</a>)</li>
<li>Wood spec energy = 4.50 kWh/kg (<a href="https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html" rel="nofollow noreferrer">engineeringtoolbox.com</a>)</li>
<li>Wood spec CO2 = 1.83 kg CO2/kg fuel (<a href="https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html" rel="nofollow noreferrer">engineeringtoolbox.com</a>)</li>
<li><span class="math-container">$\Rightarrow$</span> wood burnt = 167.2 Mt = <span class="math-container">$1.67\times10^{11}$</span> kg</li>
<li><span class="math-container">$\Rightarrow$</span> energy released <span class="math-container">$\approx 7.525\times10^{11}$</span> kWh

<ul>
<li>1KWh = <span class="math-container">$3.6\times 10^{-6}$</span> TJ</li>
<li>= <span class="math-container">$2.708\times10^{6}$</span> TJ</li>
</ul></li>
<li>Hiroshima = 54-75 TJ (<a href="https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html" rel="nofollow noreferrer">wikipedia</a>)</li>
<li><span class="math-container">$\Rightarrow$</span> Aus Bushfires <span class="math-container">$\approx$</span> 36k-50k Hiroshima bombs worth of heat.</li>
</ul>

<p>According to the <a href="https://nypost.com/2020/01/15/ocean-is-warming-at-rate-of-5-hiroshima-nukes-a-second/" rel="nofollow noreferrer">New York post</a>, the ocean (which accounts for 90% of the earth's warming budget) is warming at a rate of around 5 Hiroshimas a second, which would suggest that the <strong>total heat from the bushfires would be eclipsed by global warming forcing in around 3 hours</strong>.</p>

CC BY-SA 4.0
2020-02-13T08:15:42.230Z
Oooh that's interesting! Do you want to swap and check each other's working?
Will
CC BY-SA 4.0
2020-02-17T16:53:09.613Z
With other words: The part of the total fire loading you are expecting to be burned is ~9 t/ha (wood/other organic material) and Will estimates 675 t/ha (wood/other organic material). (BTW: compare this with Germany, which has an average "timber stock" of ~160t/ha and Sweden one of ~80t/ha (this is per total area not only forests).
klanomath
CC BY-SA 4.0
2020-02-18T01:20:40.007Z
Thanks @klanomath, fixed again. Still has a 2-order-of-magnitude difference from Will's answer. If there are more mistakes, this should probably become a community wiki ;)
naught101
CC BY-SA 4.0
2020-02-18T01:54:37.417Z
@naught101 Do you have any figures of the forest/grassland ratio of the burnt areas? In my opinion 675 t of burnt material/ha (Will's estimation) appear excessively high. BTW California's 2017/2018 wildfires released an estimated average of ~60 t CO₂/ha (~33 t wood&other organic material/ha).
klanomath
CC BY-SA 4.0
2020-02-18T02:50:34.250Z
No, sorry. I expect that would be really hard to estimate. The burn area polygons that come from the RFS are pretty course, and the on-the-ground situation is a *lot* more patchy, in my experience. Also Australian vegetation is very patchy anyway, there aren't many areas on the Divide that have homogenous forests. I guess you could get a really rough estimate by combining the RFS maps with e.g. [this Tree Cover dataset](https://glad.umd.edu/dataset/global-2010-tree-cover-30-m). I'd probably reduce the estimate anywhere hilly (and especially south-facing) by 10-40%..
naught101
CC BY-SA 4.0
2020-02-18T08:48:29.860Z
@naught101 I'm reasonably sure I've pitched it a bit high - The fuel volume is based on a mature eucalyptus stand with a generous fudge for branch-wood and under-storey vegetation (so misses out scrub woodland or immature stands). I've also assumed that 90% of it will be burned (which is probably too generous) So mine is probably a extreme high-end estimate
Will
CC BY-SA 4.0
2020-02-19T02:20:40.820Z
@Will Yep. Still, the end result of "somewhere between 2.7e6 (mine) and 2.3e8 TJ (yours)" actually seems like fairly reasonable constraints, given the complexity of the problem :)
naught101
CC BY-SA 4.0
2020-02-13T03:37:16.983Z
2020-02-18T01:18:43.837Z
2020-02-18T01:18:43.837Z
naught101
<p>How much heat was released from the 2019-2020 Australian bush fires? And is that likely to have a measurable impact on global atmospheric heat content?</p>

<p>Maybe as a secondary question: How much impact will the CO2 released by the fires have? And (maybe a bit to hard to answer) how much will regrowth draw down?</p>

CC BY-SA 4.0
2020-02-12T09:08:40.893Z
It should be possible to get an estimate by doing something like (energy per mass of wood) x (mass of wood per hectare) x (burnt area). An example here: http://large.stanford.edu/courses/2017/ph240/timcheck1/
Jean-Marie Prival
CC BY-SA 4.0
2020-02-12T09:20:39.740Z
You don't know the mass of wood burned per hectare, not all the wood in the burned area was consumed. Any "estimate" would be no more than a guess.
Michael Walsby
CC BY-SA 4.0
2020-02-12T09:39:55.313Z
That's how scientists make estimates all the time. For instance, when University of Sydney announced one billion animals killed in bushfires, they just did (average animal density) x (cleared area): https://sydney.edu.au/news-opinion/news/2020/01/08/australian-bushfires-more-than-one-billion-animals-impacted.html Of course it does not mean that exactly one billion animals died, but it tells us that it's not 100 millions, and it's not 10 billions. It gives us an *order of magnitude*. You can do the same with the energy released.
Jean-Marie Prival
CC BY-SA 4.0
2020-02-13T23:42:50.573Z
This [Washington Post article](https://www.washingtonpost.com/weather/2020/01/24/australia-bush-fires-have-nearly-doubled-countrys-annual-greenhouse-gas-emissions/) gives a partial answer: 400 million tonnes of CO2 emitted by January 24th ... but it is not a total. The impact of the ash, some of which **may** have made it to Antarctica, could be greater than the impact of the CO2 emitted (by changing albedo) -- but that is just my speculation.
M Juckes
<climate-change><co2><wildfire><fire>
How much heat was released from the 2019-2020 Australian bush fires?
naught101
# How much heat was released from the 2019-2020 Australian bush fires?

(Asked by: username_0 on 2020-02-12)

How much heat was released from the 2019-2020 Australian bush fires? And is that likely to have a measurable impact on global atmospheric heat content?

Maybe as a secondary question: How much impact username_4 the CO2 released by the fires have? And (maybe a bit to hard to answer) how much username_4 regrowth draw down?

**Tags:** climate-change, co2, wildfire, fire

> **Comments:**
> **username_1**: It should be possible to get an estimate by doing something like (energy per mass of wood) x (mass of wood per hectare) x (burnt area). An example here: http://large.stanford.edu/courses/2017/ph240/timcheck1/  
> **username_2**: You don't know the mass of wood burned per hectare, not all the wood in the burned area was consumed. Any "estimate" would be no more than a guess.  
> **username_1**: That's how scientists make estimates all the time. For instance, when University of Sydney announced one billion animals killed in bushfires, they just did (average animal density) x (cleared area): https://sydney.edu.au/news-opinion/news/2020/01/08/australian-bushfires-more-than-one-billion-animals-impacted.html Of course it does not mean that exactly one billion animals died, but it tells us that it's not 100 millions, and it's not 10 billions. It gives us an *order of magnitude*. You can do the same with the energy released.  
> **username_3**: This [Washington Post article](https://www.washingtonpost.com/weather/2020/01/24/australia-bush-fires-have-nearly-doubled-countrys-annual-greenhouse-gas-emissions/) gives a partial answer: 400 million tonnes of CO2 emitted by January 24th ... but it is not a total. The impact of the ash, some of which **may** have made it to Antarctica, could be greater than the impact of the CO2 emitted (by changing albedo) -- but that is just my speculation.  

---

## 2 answers

### Answer by username_4 on 2020-02-12. Score: 9

Right. We can make some estimates of the scale of the problem, but they username_4 come with a healthy margin of error.

* If we assume that wood has a calorific value of 18.5 GJ/t (from the [phyllis2](https://phyllis.nl/Browse/Standard/ECN-Phyllis) database)
* The area burned is 18.6 Mha (from Wikipedia [here](https://en.wikipedia.org/wiki/2019%E2%80%9320_Australian_bushfire_season))
* The standing volume of material is circa 1500 m3/ha (an educated guess based on Eucalyptus values in [Forest Yield](https://www.forestresearch.gov.uk/tools-and-resources/forest-yield/))
* The density of timber is circa 0.5t per dry m3 (from [Forest mensuration handbook](https://www.forestresearch.gov.uk/research/forest-mensuration-a-handbook-for-practitioners/))
* and only 90% of that material actually burns (a guess)

Then:

There's around 675 tonnes of material burned per ha releasing 12,150 GJ of energy which is equal to 225,990,000 TJ for the total area or 3,587,143 Hiroshima bombs (at [63 TJ each](https://en.wikipedia.org/wiki/Little_Boy))...

This is a (very) rough calculation, but it gives a scale of the amount of heat released. This is about 10 day's worth of [solar constant](https://en.wikipedia.org/wiki/Solar_constant) radiation over the same area, so it might appear in local temperature readings, but bear in mind that 1) there was already unusually high temperatures in the area, and 2) fires like this produce a lot of smoke which username_4 have had an effect on the local radiation budget.

In terms of all that CO2, you can expect it to be reabsorbed by the surrounding biosphere which is described in the impulse response function described in the IPCC AR5 WG1 CH8 technical supplement ([8.SM.11.1 Equations for the Global Warming Potential](https://www.ipcc.ch/site/assets/uploads/2018/07/WGI_AR5.Chap_.8_SM.pdf)). You can also expect the burned areas to regrow - which username_4 absorb CO2 as well. Depending on rates of growth, I would expect this to take several decades. - but there is a *lot* of very complex processes, so this is open to a lot of discussion!

Hope this helps.

> **Comments:**
> **username_5**: +1 for linking back to the sources of your estimates!  
> **username_6**: I feel like the most important part of this answer is buried in the middle paragraph: "This is about 10 day's worth of solar constant radiation over the same area..." So the heat generated is basically negligible in terms of global climate. I'm fairly sure that the CO2 released username_4 have a bigger effect before it is reabsorbed, but I don't know the numbers for that.  
> **username_7**: Query regarding unit in first bullet point, should the unit GJt be GJ/t?  
> **username_7**: It's something I learnt from other users, either here or on other SE sites. To do a superscript, bound the item to be superscripted with *<sup> ... </sup>*; i.e. for cubic meters type this: *m<sup>3</sup>*. Similarly, for subscripts used *<sub> ... </sub>*; i.e. for carbon dioxide type *CO<sub>2</sub>*. When I see someone has created some interesting formatting of text I pretend to edit the post. I then see the Matjax formatting in the text box & note it. I then cancel my pretend edit. It's a quick way of learning some interest ways to do Mathjax formatting.  
> **username_1**: There is an easier way: just put a dollar sign to enter equation mode, then underscore _ or circumflex ^ for subscript or superscript, then the number, and finally another dollar sign to leave equation mode. If you want several numbers in a row, just put them between curly braces. It's all explained here: https://earthscience.meta.stackexchange.com/q/371/18081  
> **username_7**: @username_1: The $ works, but it also changes the font.  
> **username_0**: I posted a different method of calculation below, with different sources for most things, and starting based on CO2 estimates from NASA (probably the main discrepancy?). The figures are out by 3 orders of magnitude. I'd love a review :) The things that stick out to me in your calculation as a major difference is that the burnt areas likely include a *lot* of grass land, and so the biomass/hectare is likely overestimated. Also, I think 90% figure should probably be much less than 50% in most areas - the bulk biomass in forests is in tree trunks I think, many of which do not burn.  
> **username_8**: Given the estimates/uncertainties in the calculation saying *225,990,000 TJ* is not correct. Better would be 226 EJ.  
> **username_4**: Fair enough, think @username_0 and I need to check each other's working in any case  

---

### Answer by username_0 on 2020-02-13. Score: 4

**EDIT**: As pointed out by username_1 and username_9 in the comments, I originally misread the specific heat of wood as per tonne, rather than per kilogram, and also used the wrong conversion between TWh and TJ.

Here are my rough calculations, based on CO2-release estimates from NASA:

* 306 MtCO2 ([wikipedia](https://en.wikipedia.org/wiki/2019%E2%80%9320_Australian_bushfire_season#Environmental_effects))
* Wood spec energy = 4.50 kWh/kg ([engineeringtoolbox.com](https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html))
* Wood spec CO2 = 1.83 kg CO2/kg fuel ([engineeringtoolbox.com](https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html))
* $\Rightarrow$ wood burnt = 167.2 Mt = $1.67\times10^{11}$ kg
* $\Rightarrow$ energy released $\approx 7.525\times10^{11}$ kWh
  + 1KWh = $3.6\times 10^{-6}$ TJ
  + = $2.708\times10^{6}$ TJ
* Hiroshima = 54-75 TJ ([wikipedia](https://www.engineeringtoolbox.com/co2-emission-fuels-d_1085.html))
* $\Rightarrow$ Aus Bushfires $\approx$ 36k-50k Hiroshima bombs worth of heat.

According to the [New York post](https://nypost.com/2020/01/15/ocean-is-warming-at-rate-of-5-hiroshima-nukes-a-second/), the ocean (which accounts for 90% of the earth's warming budget) is warming at a rate of around 5 Hiroshimas a second, which would suggest that the **total heat from the bushfires would be eclipsed by global warming forcing in around 3 hours**.

> **Comments:**
> **username_4**: Oooh that's interesting! Do you want to swap and check each other's working?  
> **username_9**: With other words: The part of the total fire loading you are expecting to be burned is ~9 t/ha (wood/other organic material) and username_4 estimates 675 t/ha (wood/other organic material). (BTW: compare this with Germany, which has an average "timber stock" of ~160t/ha and Sweden one of ~80t/ha (this is per total area not only forests).  
> **username_0**: Thanks @username_9, fixed again. Still has a 2-order-of-magnitude difference from username_4's answer. If there are more mistakes, this should probably become a community wiki ;)  
> **username_9**: @username_0 Do you have any figures of the forest/grassland ratio of the burnt areas? In my opinion 675 t of burnt material/ha (username_4's estimation) appear excessively high. BTW California's 2017/2018 wildfires released an estimated average of ~60 t CO₂/ha (~33 t wood&other organic material/ha).  
> **username_0**: No, sorry. I expect that would be really hard to estimate. The burn area polygons that come from the RFS are pretty course, and the on-the-ground situation is a *lot* more patchy, in my experience. Also Australian vegetation is very patchy anyway, there aren't many areas on the Divide that have homogenous forests. I guess you could get a really rough estimate by combining the RFS maps with e.g. [this Tree Cover dataset](https://glad.umd.edu/dataset/global-2010-tree-cover-30-m). I'd probably reduce the estimate anywhere hilly (and especially south-facing) by 10-40%..  
> **username_4**: @username_0 I'm reasonably sure I've pitched it a bit high - The fuel volume is based on a mature eucalyptus stand with a generous fudge for branch-wood and under-storey vegetation (so misses out scrub woodland or immature stands). I've also assumed that 90% of it username_4 be burned (which is probably too generous) So mine is probably a extreme high-end estimate  
> **username_0**: @username_4 Yep. Still, the end result of "somewhere between 2.7e6 (mine) and 2.3e8 TJ (yours)" actually seems like fairly reasonable constraints, given the complexity of the problem :)  

---

