Temperature

Trends within Varibility

Climatological averages and trends need to be seen relative to the inter-annual variability

Change and Significances

Trends determined on different length of timeseries can be a good indicator of change. A period dominated by natural variability (low trend) can be seen in contrast to the emergence of an (anthropogenically) forced trend.

Future changes and scenarios

Global climate change means that temperatures are also rising in Bangladesh. If greenhouse gas emissions continue to rise unchecked, a further increase in the annual average temperature of around 2–3°C is possible by the middle of this century.

Average temperature increases in Bangladesh are broadly in line with the IPCC’s global projections. When factoring in warming prior to the baseline period of 1986–2005 (i.e. when calculating temperatures against pre-industrial levels) the warming experienced in Bangladesh will breach the 2°C threshold by the end of the century under all RCPs except RCP2.6. This highlights the importance of achieving lower global emissions pathways. Warming in Bangladesh has two distinctive features. First, warming in both daily maximum and minimum temperatures considerably outstrips average warming, typically rising around 10%–20% higher. Second, warming is much stronger in the winter season (December-February) than the summer (June-August), typically 10%–30% higher. These features have the potential to amplify the impacts of temperature rises on human health and livelihoods

Projected Average Annual Temperature in Bangladesh Under RCP2 6 (Blue) and RCP8 5 (Red) Estimated by the Model Ensemble Shading Represents the 10th and 90th Percentile of the Multi-Model Range

Figure: Projected Monthly Mean Temperature, in Relation to the Historical Reference Period, 1986–2005, for Bangladesh for the Period 2040–2099 under RCP8 5 The Value Shown Represents the Median of the Model Ensemble with the Shaded Areas Showing the 10th–90th Percentiles

The further changes to the climate depend on the global emissions of greenhouse gases. The values listed below show how temperatures are projected to change with climate change mitigation (emission scenario RCP2.6) and without mitigation (RCP8.5) in the near future (2035), by the middle of the century (2060), and towards the end of the century (2085).

Table: Projected Anomaly (Changes °C) for Maximum, Minimum, and Average Daily Temperatures in Bangladesh for 2040–2059 and 2080–2099, from the Reference Period of 1986–2005 for All RCPs The Table is Showing the Median of the CMIP5 Model Ensemble and the 10–90th Percentiles in Brackets (CCIKP, 2021)

	RCP 2.6	RCP 4.5	RCP 8.5
Possible around mid-century	1.1( -1.3, 3.7)	1.5 (-0.9,3.9)	1.9 (-0.5, 4.4)
Possible by the end of the century	1.2 (-1.3, 3.8)	2.2 (-0.3, 4.9)	3.9 (1.4, 6.7)

WBG Climate Change Knowledge Portal (CCKP, 2021). Climate Data: Projection. Bangladesh. URL: https://climateknowledgeportal.worldbank.org/country/bangladesh/climate-data-projections

If greenhouse gas emissions continue to rise unchecked (RCP8.5), temperatures could rise by up to an additional 2°C by the middle of this century. However, if successful efforts are made to quickly reduce greenhouse gas emissions worldwide (RCP2.6), the temperature would still rise further by the middle of this century, but the increase would likely be limited to around 1.1 °C. The differences between the emission scenarios increases towards the end of the century.

Table: Projections of Average Temperature Anomaly (°C) in Bangladesh for Different Seasons (3-Monthly Time Slices) Over Different Time Horizons and Emissions Pathways, Showing the Median Estimates of the Full CCKP Model Ensemble and the 10th and 90th Percentiles in Brackets27(CCIKP, 2021)

Scenario	2040-2059		2080-2099
	Jun-Aug	Dec-Feb	Jun-Aug	Dec-Feb
RCP 2.6	0.6( -1.1, 2.9)	1.5 (-0.7,2.8)	0.6 (-0.9, 3.2)	1.7 (0.7, 2.9)
RCP 4.5	1 (-0.6,3.3)	1.6 (-0.4, 2.9)	1.6 (-0.1, 4.2)	2.3 (0.3, 4.0)
RCP 8.5	1.6 (0.0, 4.0)	2.2 (0.0, 3.8)	3.4 (1.7, 5.9)	4.5 (2.4, 6.2)

WBG Climate Change Knowledge Portal (CCKP, 2021). Climate Data: Projection. Bangladesh. URL: https://climateknowledgeportal.worldbank.org/country/bangladesh/climate-data-projections

Model Ensemble

Climate projections presented in this document are derived from datasets available through the CCKP, unless otherwise stated. These datasets are processed outputs of simulations performed by multiple General Circulation Models (GCM) (for further information see Flato et al., 2013).28 Collectively, these different GCM simulations are referred to as the ‘model ensemble’. Due to the differences in the way GCMs represent the key physical processes and interactions within the limate system, projections of future climate conditions can vary widely between different GCMs, this is particularly the case for rainfall related variables and at national and local scales.