**4.1. Weather models predict**


#### **Figure 4.**

*Global average projected surface air temperature changes (°C) above the 1986–2005 average (dark purple zero line) for the years 2000 to 2100. Temperature changes inside the graph and to the right of the graph are based on dozens of climate models run with different scenarios, based on representative concentration pathways (RCPs). Each scenario describes how the average temperature will change based on different concentrations of greenhouse gases and various forcing agents. The black line shows global temperature change during the twentieth century. The shaded bars on the right side of the figure indicate the likely range of temperature change for each scenario. The thick solid bar within each shaded bar gives the best estimate for temperature change by the years 2081–2100 for each scenario. (see table 18.1 for additional information on the four RCPs.) (source: Adapted from the summary for policymakers, climate change 2013: The physical science basis. Contribution of working group I to the fifth assessment report of the intergovernmental panel on climate change, 2013. Reprinted by permission of the intergovernmental panel on climate change).*

The reaction of diseases and pests to climate change can be directly and indirectly. The indirect reaction includes changes in crop type, crop soils, and agricultural operations as well as changes in plant and animal natural habitats that occur after climate change. Thus, changes will occur based on the resources required for pathogens and pests [6].

Under the 2015 Paris Agreement, countries agreed to reduce greenhouse gas emissions to reduce the rate of global average temperature rise to below 2 degrees, above pre-industrialization levels, and attempt to reduce this to 1.5 degrees above industrial levels.

While the overall intention to strengthen the global response to climate change is clear, the Paris Agreement has not specified exactly what the "average global temperature" means, or what period of history should be considered "pre-industrial." To answer the question of how close we are to 1.5 degrees of warming, we must first clarify how both expressions are defined in this special report [7]. The change in global temperature relative to 1850–1900 based on different scenarios (RCP) is shown in **Figure 4**.

**Figure 5** represents that human-induced warming in 2017 has reached almost 1 degree Celsius above pre-industrial levels. At the current rate, global temperatures will reach 1.5 degrees Celsius around 2040. The 1.5 degrees Celsius path shown here

**Figure 5.**

*Human-induced warming and predicting its future trend)IPCC, 2019, P82).*


*\* Temperature changes are relative to the average surface air temperature for the period 1986–2005. (Ahrens and Robert, 2014, p. 523).*

#### **Table 1.**

*Projected average surface air temperature increases: Ranges and best estimates for the period 2081–2100, using six representative concentration pathways (RCPs)\*.*

includes emissions reductions that start immediately and reduce carbon dioxide emissions to zero by 2055 [8]. Each set of simulations uses a different representative concentration pathway (RCP), describing how the total radiant changes over this century (**Table 1**) [2].
