Given the vastness and intensity of the bushfires that have been going on in Australia for weeks now, to the point they are generating their own weather and having an impact thousands kilometers away from their origin, an analogy with volcanic eruptions spurred to my mind and I wondered: could the net effect of these bushfires actually be a measurable cooling down of global temperature, as it happened with Mount Pinatubo, at least in the short term?
Well, the amount and intensity of wild fires are a direct outcome of global warming, that's not really news.
According to this article that cites a work i can't find, until the mid of December 2019 the Australian fires emitted ~250million tons of carbon, ~50% of Australia's yearly production. A recovery in the coming decades is unlikely, because the ecosystem is already compromised. It is "too optimistic" to assume that the forests will regrow and they will "never end up accumulating as much carbon as they had before". Instead, large areas of burning forests must more and more be seen as a biospheric component that can turn from a carbon sink to a source.
Here's an example (sorry paywalled, but the abstract has the interesting points and it is peer reviewed) for boreal forest fires, where fires can lead from net accumulation over several fire events to a net loss, leading to a positive feedback. A similar process is expected for the Amazon rain forest fires.
To the question: an exact answer seems to be difficult. It depends on how much aerosols end up where in the atmosphere and stays for how long. The effect can be modelled: Here, a fire aerosol laiden atmosphere's lower 6km can be warmed because they become a heat trap. The trap is caused because aerosols have a stabilizing effect on the upper atmosphere. A forest fire's plume has a different composition than a volcanic eruption !
This paper describes a similar effect, the absorption of solar radiation by carbon can heat the atmosphere.
I am aware that there may be other effects, inclduing atmospheric cooling, but i leave that part to somebody else. All in all, the negative effects of carbon release and the potential loss of regenerative abilities of the biosphere - because of drought, erosion, loss of biodiversity and the ecosystem, soil sterilization, invasive organisms as well as the difficulties to respond in time because of the sheer area affected by fire (all depending on intensity, duration and area) - by far outweigh any cooling effects of wild fires.
It is unlikely that the Australian fires will produce enough particulates by themselves to induce measurable global dimming, but we can't be sure because the fires are not yet finished and could continue for months. Another thing to remember is that Australia is not the only country to have major wildfires, so it seems probable that the combined effects of all these fires on global dimming may be measurable.
People worried about all the CO2 being poured into the atmosphere by these wildfires should bear in mind that if the drought is followed by a wet period,the forest will regenerate and recapture an amount of CO2 equivalent to the amount they have released. Major eruptions like Pinatubo release colossal amounts of CO2, but unlike burning forests have no mechanism whereby they can suck most of it back in the fulness of time. They also release vast quantities of dust particles high into the atmosphere, accompanied by large amounts of sulphur dioxide which reflects solar radiation back into space, so that explains the cooling effect such major eruptions have. It usually doesn't last very long.