Well, my username is Yarnabrina 
Can you please elaborate? Do you want something like geom_smooth? In that case, you can do something like the following. This can be made better, but I don't know much about loess.
df <- data.frame(Date = c(1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989, 1990,
1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000,
2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010,
2011, 2012, 2013, 2014, 2015, 2016, 2017),
Temp = c(-0.2, -0.1, -0.2, -0.7, -0.3, -0.4, -0.7, -0.8, -0.8, -0.2,
0.2, -0.4, 0.1, -0.1, 0.2, -0.1, 0.4, 0.5, 1.0, 0.2,
0.2, 0.2, 0.1, -0.6, 0.6, 0.6, 0.2, 0.2, 0.5, 0.2,
0.3, 0.3, 0.2, 0.4, 0.0, 0.6, 0.5))
with(data = df,
expr = {
plot(x = Date,
y = Temp,
pch = NA_integer_)
polygon(x = c(min(Date), Date, max(Date)),
y = c(0, Temp, 0),
col = "red")
usr <- par("usr")
clip(x1 = min(Date),
x2 = max(Date),
y1 = min(Temp),
y2 = 0)
polygon(x = c(min(Date), Date, max(Date)),
y = c(0, Temp, 0),
col = "blue")
do.call(what = clip,
args = as.list(x = usr))
lines(x = loess.smooth(x = Date,
y = Temp,
span = 0.25),
col = "green",
lwd = 2)
})

For a ggplot solution, you might want to look at this SO post. You'll have to change this for your own data, of course.